I'm concerned about my diesel. She doesn't feel right.

The sound of the engine at idle is a little harsher than I remember it and the engine seems to shake a little differently, not the usual harmonic. There also seems to be a distant thump sound in the engine especially when hot after a hard run.
These changes are mostly sublte, but I've been driving the car forever so I a) am too close to notice a difference and/or b) should know how it's supposed to be.

I'm going to have my mechanic perform a compression and leak test if necessary.

Engine has 300,000 miles
New chain, filters, IP timing correct

How do you diagnose a worn IP?

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6