The C280 is a 722.4 trans, which is just a 722.3 with small differences. It could be a B2 piston since I've heard this sing-song before. Since I'm not sure, I will tell you this it most likely is more than just an adjustment.

I recall the build thread from another forum. So it probably wasn't parked because of engine related issues alone and more like they wanted to unload it for more than they described or "forgot".

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k