[dsraven]

if you pull the filter and find bad news it would be in your best interest to pull the engine out and completely disassemble the engine and see what you have. I have seen some guy's idea of a rebuilt. some are a car wash and some engine paint. some are dissassemble, ball hone,, rering and bearing and assemble without even checking ring end gap or bearing clearances. some are a complete, properly checked, cleaned, spec'd rebuilt like you would expect when told it is redone. I installed an engine for a fiend who had a reputable engine builder do his 350 into a 383. it arrived all nice and fresh looking. when I poured coolant in there was a leak right away at the rear somewhere. turned out the frost plugs weren't even replaced let alone the block hot tanked. there was a whole load of problems with the engine including stripped bolt holes, leaky seals etc. best to take it apart and see for yourself if it comes to that. hopefully it is something simple and you can carry on.
I have found it is best to see the bills for the work or else make the deal as if the engine were an old clunker. unless the guy has bills for new parts and actual specs for clearances, work done etc, you just can't tell. some guys honestly believe what they have done constitutes a "rebuilt" engine. one easy way to tell if it has at least had some work is with a boroscope through a spark plug hole and through the oil filler to see what that part looks like.
anyway, hopefully it is an easy fix and it doesn't keep you up at night.
keep us posted