I try to clean it as I take it apart. Parts that come off can go in a bucket (recoil bar/clutch covers clutch oil pump...) Water should not get past the seals unless they are shot. Clean around the muffler before you pull it off. Once you have the clutch/flywheel off you can scrape the gunk out then hit things with the diesel/brushes. Diesel won't hurt a thing. Try to avoid getting any grime/dirt into the intake/exhaust. An oiled piece of rag should plug those up.
Here is a 038 I did and it's clean enough to pull the jug. Still be careful then as you never get every bit of grime around base of jug (see picture).
Have some rags or towels handy to stuff in around the crank.
This one I had to split cases as ate some bearing material.
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Here is a 026 I got for $90. Ran/Runs great but it was one of the filthiest saws I'd seen. That is after a good bath
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