I opened up driver's side cover (left) and here is my tensioner, attached. I think date on it says: 8/06, so I suppose it was updated. Also, it looks like the engine front cover also came off at some point, because the hood has sharpie markings around the hinges and also I saw some extra silicone, down the main chain area.

I do have one issue though. After replacing valve cover gasket and all other minor ring gaskets, right bottom corner still leaks oil on exhaust manifold and it does it, as soon as engine warmns up for a minute, or two.
Can there be a crack in valve cover?

 

Couple of things-

-Normally a bit of oil spill on the exhaust manifold when the covers are off. This will burn off eventually after some smoking. Are you sure it is fresh oil leaking out?
-Did you torque the cover from the center bolts outward to the ends? If not, I would loosen the bolts and retorque them in that fashion.

 

I checked that it was not a burn off, fresh oil kept coming on one particular spot, same one where it leaked before I put in new gaskets.
I did not torque outward, but did do it in stages. Previously cover was overtightened, some bolts were hard to move and two of the 7mm bolts, holding ignition cover, were swapped for 8mm. This tells me that someone was already there.

What do you think of the tensioner, it looked like its body was aluminum?

 

Yup, it looks like the tensioners were updated.

 

My XK8 had a cracked cover. If I remember right the replacement price is not too bad when compared to the replacement cost of the gaskets alone.

Did you add a dab of silicone to the joint where the front cover meets the head?

Or by "right bottom corner" do you mean the rear lower corner? That's where mine was cracked.

 

I got it to seal, finally! It was not cracked, just did not sit well.
Also, small breather on the left cover was almost completely clogged by sludge, even though engine surfaces seemed ok and not too dirty.
I opened up oil separator, washed those wire sponges and entire valve cover from the inside, so I do not regret taking it apart again.

 

Excellent...glad to see you getting those boxes checked off !

 

That appears to be a "plastic" tensioner in the picture. If so REPLACE IT!!!!!
No matter what the date stamp says. If it has an alloy metal body you are good to go. Hope you determined that before you buttoned it up. If not...you are not done!! The guide on top of the tensioner looks red, the new metal bodied ones have a white slider on top.
My sliders were severely galled and had cracks in the plastic tensioner body. I also replaced the main chain guides as they had cracks, along with Primary tensioners and new chains. You really should do it all in my opinion. Car had 65k miles.
Everyone trying to "get by" with just the secondary tensioner replacement is playing roulette IMO!!!!

Mish_Mish check it again, be sure it has metal body (4.2L type). There was an "improved" plastic one but the final fix was a metal one.

 

Steve, 100% agree about changing the tensioners...but I think he already has the metal ones. Even the plastic ones (see photo) started out white...heat, age and engine oil turn them red.

 

Yes, these are metal body, it is oil deposit that made them reddish, slider head was origanially yellowish, under the sludge.
I will be checking another side and replacing gasket + plugs, so will see another side soon.
Also, it looks like main chain tensioner body was also metal, looking from the side. Also, I noticed some sloppy silicone sticking from under the front engine cover, towards the main chain, so maybe nice Cuban mechanic got that done for me, back in florida