I would go to another shop, not because I think the one you're using is trying to rip you off or anything, but because he may just not see the problem and sometimes someone with a different perspective can spot a problem like you have. I can't think that it is a major problem ($$$$) since the car runs well and I guess doesn't use much oil or drink coolant?

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k