I recently found a dirty moist spot on my driver's cylinder head. Could it be a leaking gasket? Cars runs fine, doesn't overheat, but it does loose coolant about half a inch per month.

 

I don't see anything about what engine you have, what year or configuration you have, but one thing for sure is that you have a leak.
It's most likely the valve cover gaskets that's causing what you're looking at.
That's independent of whether or not you have a head gasket problem.
But so is the possibility of coolant system leaks that could explain the loss of coolant, more likely and preferable to a blown head gasket.

 

Sorry about that. 2016 Jaguar xjl 3.0 awd

 

How many kilometres/miles are shown on the instrument cluster?

Oil leak may be from the cam cover gasket.

Any loss of coolant is a serious situation on the AJ126. After a cold soak, preferably overnight, use a cooling system pressure tester to pressurise the system to 1 bar for 15 minutes. If the pressure tester gauge shows any loss of pressure, search for leaks. Remember to check the water outlet pipes directly under the supercharger snout, the water pump, and the overflow tank for leaks.

 

It doesn't seem to be leaking anything from above it's just that area between the head gasket area. I was think of either using the pressure test or the "special liquid" that changes color.

 

Oh, I was thinking about the gasket up top. I didn't realize the side or front of the head has a cover where the timing chain is located. I would pray that's the problem because I'm getting 10k quotes to rectify the situation which is ridiculous. My warranty only covers up to 5k. Guess I won't be getting a pulley upgrade and tune no time soon 😞

 

We're all hoping and/or praying that it's the expected valve (AKA camshaft) cover on yours too.
I had to replace the head gaskets on one of the two V8 AJ133 engines we have, and IIRC it cost me a little under $1k including special tools I had an excuse to had to buy to do the job.. Actually I would be less accepting to have bought the tools except for the fact that I have 2 AJ133s and might possibly need to do the job again on one or the other.
But the pic you posted looks like a plain old camshaft cover leak, which are expected after years & miles - part of normal long term maintenance for any engine.
Another common source of oil leakage is from the vacuum pump on the front of the engine, just below & to the left of the crankshaft as you look at the front of the engine. If you look up "vacuum pump" and look for posts that discuss it in the forum, you'll find lots of good info that we've experienced & replaced the gaskets of the pump to fix that common leak.
That is lower on the engine but it can still sling oil around the front of the engine.
A head gasket is almost always an internal leak that doesn't usually let oil out, but instead lets oil leak into the coolant passages, or into a combustion chamber, or more often in an "open deck" block like the AJ133 (or the 6 cylinder equivalent) lets coolant leak into the combustion chamber, or an oil passage.
But as NBCAT wrote above, the health of the coolant system can't be emphasized enough. If it's not kept healthy, a blown head gasket is surely an expensive risk.

 

After a closer look it doesn't look real fresh. I removed the air intake and was able to get a couple of better pics. The belly pan has seepage on it as well which is circled in the 2 photos.

 

Clean all the oil and dirt off and then watch what comes back. Taking pictures of dirt and oil is of no value.
Have you got the car in the air and taken the belly pans off to inspect?

You got good suggestions above and the gear driven vacuum pump is a prime suspect as well as the cam cover gaskets.
Less likely are the timing cover gaskets but again it's all covered in dirt and oil so you can't tell anything.

Please, please listen to NBCat and 12jagmark about your car losing coolant! The number one cause of engine failure in Jaguars (Especially the late model 5.0 and 3.0 SC models) is cooling system failures. Your new but do some searchers and consider getting all the failure prone plastic cooling parts swapped out to the much better after market Aluminum ones. There are a number of parts that are known failure points.

Also you can't trust the temperature gauge in the dash as it won't move until it's too late. Many of us use after market scanners to monitor the actual coolant temperature.
So do keep a close eye on coolant levels and get the system pressure tested as suggested above.
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Thank you all for the guidance. Seems like I have a bit of work ahead of me as I have to replace the coupler in the supercharger. I've searched to get info on the driver's timing cover (cam cover) removal with little results. I'm trying to make sure if the cover can be removed without removing the valve cover? Is there a gasket or must I use rtv?

 

Here is a link to the Technician course for the AJ133 engine:

https://www.dropbox.com/scl/fi/kbiot...=y3gtjmow&dl=0

The 3.0 litre AJ126 is similar in layout.

 

The camshaft cover and 'valve cover' are the same component. Bear in mind the camshaft cover(s) can only be removed once the fuel injectors and ignition coils have been removed beforehand.

There are several gaskets that must be replaced:

https://www.sngbarratt.com/English/#...assembly/34351

 

It's entirely possible that you have two separate issues. I would check for oil in the coolant, and coolant in the oil. Can you recognize the distinct aroma of coolant? If you are unfamiliar with this unique odor, ask a knowlegable person to sniff under your hood.
Agree with previous posters that your decrease in expansion tank level requires immediate attention.

 

Well, doesn't seem to be a head gasket leak, whew.

 

That's a big relief!
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Yea. I have to change the supercharger coupler so I'll upgrade the coolant pipes as well. Just came from a 800 mile trip and the drive was wonderful and the 30 mpg put a smile on my face. I brought a bottle of dex because I expected the coolant level to drop, but it didn't at all.

 

OK, so you don't have exhaust gasses in the coolant. That's one possibility checked off your list.