JeffS7444
Well-known
If it was me, even if it looks ok, the very first thing I would clean is the 45 degree surface of the split prism. I've cleaned that before on an SP finder and the focus patch went from unusable to really good. Just by cleaning that surface alone.
Yes I'll do that first. In normal room light I thought that prism looked clean, but with a good strong light - yuck! Looks like it's covered in a light haze of grease.