I'm tearing into my newly-acquired Panther, which uses a 1974 XJ6 engine. The car only has 10,100 miles, but leaks a lot (surprise!..Jaguar).
I don't expect to find any significant wear, but plan to do a complete teardown and rebuild with new gaskets, seals etc.
Who do you recommend for parts for a Jaguar of this vintage?

 

With that few miles, I suspect a lot of the leaks are simply due to lack of use. I once bought an E Type that had sat for 17 years and leaked everywhere. I started driving it and slowly the leaks dried up as the seals were rewetted and swelled again.

Not everything can be dealt with that way, but generally the crankshaft seals can dry up. For the rest, I've had great luck using Loctite 515 or 518 flange sealer on metal to metal parts, such as the cam covers and breather cover on the front, as well as the cam oil feed lines. I've also used Loctite 567 thread sealant for things like the oil pressure sender to block threads and that has cured 95% of the leaks.

 

You can replace the rear main oil seal with a lipped type, there are a couple of US suppliers. I found a couple for Napoleon Solos thread.

Front main seal is a lipped type, but on some engines, Jaguar left off the oil thrower behind it. You need to put it back somehow.

Other than this, it's just a matter of new gaskets and also the copper washers below the domed cam cover nuts.

 

I have used partsgeek.com for quite a few basic parts on the 77 XJ12L I am bringing back to life after a 20 year rest.

I was surprised at the the variety of parts they have. Some of the parts are decent aftermarket suppliers, some of them are less so.

For engine gaskets, I see they have a crankcase set for $36. I might pass on that for a more established brand, but for an air filter, I would be all over it.

1974 Jaguar XJ6 Parts - PartsGeek

I think Rockauto is in the same family of supplier.

RockAuto Parts Catalog

Partsgeek has almost zero customer support. Make sure you have your order correct. They don't screw that up, but don't expect to talk to a person directly, ever.

The car I am working on has some replacement parts from Welsh Enterprises in Southeast Ohio. I called them and you get great customer support but, fairly, you pay for it.

 

For Jaguar parts that cannot be purchased on RockAuto, my go-to is Terry's Jaguar. Their prices are very competitive and their service is top notch. They also ship USPS Priority Mail when it's appropriate/cost effective, and have no minimum order.

I stay away from XKs Unlimited. They have a great selection, but they have a minimum order and they switched some products around on me... listed one brand and sent another.