Check and adjust valve clearance once a year. Before it gets cold if it gets cold where you are.

I wouldn’t bother with a compression test if it starts easily, idles smoothly and has decent power.

I wouldn’t replace the chain if it’s within a couple of three degrees of spec using the eyeball method. Check whether it has an offset key.

I wouldn’t rebuild the turbo if the engine performs. Any axial play in the turbo shaft is bad. Anything more than just perceptible radial play is bad. Any oil leaking into the compressor or turbine sections is bad. I don’t know if crankcase ventilation dumps upstream of the turbo so confirm the source if you see oil on the compressor wheel.

IIRC the 617 trap warranty replaces it once. There’s no servicing a trap. An alternative to a trap bypass is retrofitting the manifolds, turbo, downpipe and air cleaner from a pre-trap 617. You can keep the air cleaner where it is with minor modification of the turbo air inlet hose.

Sixto
98 E320s sedan and wagon
02 C320 wagon