I have squeaks from various places, too ... some are seat related ... even with well treated leather they still squeak and creak ... I think age is an issue with springs, too.
I would do compression checks as noted and then rebuild, as needed.
I am assuming you are using synthetic oil ... if not, you might try a few thousand miles on Mobil 1 just in case it can soften the seals more ... might get lucky.
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg