sgordon1; proper maintenance is paramount on cars. Especially, routine oil changes, not racing engines without proper oil flow first, and letting turbo charged engines idle for a few minutes before shutting off.
But, pistons, valves, bearings, and piston rings do wear out. Usually, compression will diminish after about 150000 miles. the car will run, but there will be compression loss. parts wear out. Especially piston rings.
So, a compression test or better, a leak down test is a necessity after 150000 miles. Regardless of whether you think the engine is okay. Just so the owner knows the condition.
I'm an audiophile, but I also am an Electrical Engineer and I restore classic cars and work on cars. (stress relief).
I own a 1970 Plymouth Barracuda (in-violet purple) that I restored (five years), a 1983 Volvo 244 Turbo that I owned since new and restored and 1995 Volvo 850 T5R also well maintained.
The 83 Volvo has 320,000 miles (completely restored. engine rebuilt, electrical, interior, exterior, etc.), the 95 Volvo has 240,000 miles, also engine rebuilt, transmission rebuilt, suspension, etc.
I maintain things. The problem is that if one waits until the engine falls out, well, that is slightly too late.
For my Monolith III speakers, I just notice a slight change in the higher registers. Something wasn't quite right to me. I replaced my panels in 2006, and since Martin Logan uses the latest technology in their replacement panel construction, my Monolith IIIs would be great. But, 10 weeks to build the new panels. they build them when they are ordered.
I thought initially that it may have been my Audio Research REF 250 amps and maybe it was time to retube them. I ordered new tubes from Upscale audio and they were supposed to be matched. but, one amp blew after I inserted the new tubes and let them warm up and biased the tubes. It took out some bias resistors and a capacitor. It also took out my DAC 8. figure out that one.
anyway, I switched amps and used my Mark Levinson 23.5 amp on the upper panels and my extremely modified Bedini 250/250 MK II amp on the woofers and guess what? still a slight loss of highs on the upper panels. I even switched speakers and used my Klipsch Forte II's and yes, something isn't quite right with the Monolith IIIs.
If you have some spare/revealing speakers you can use, try them and see/hear if there is a difference.
enjoy