Possible cause of harsh mids?

Once in a while you get that used album that sounds good except for a static like distortion on some more dynamic vocals, horns, guitar.  Just typical for some old albums?  Listening to Corea - The Leprechaun.  It's a very good sounding album, well balanced with great dynamics.  But, that annoying distortion rears its ugly head once in a while.  
Static like distortion and sibilance are two entirely different things. If the OP had heard this on other records he would have reported it. If his phono stage were overloading it would also do it on other records. I would tend to believe the OP and that it is a unique problem with this record, which means it is a problem with the record. If it walks like a duck and talks like a duck, it is usually a duck. In millercarbon's world it becomes an ostrich.  
I only have sibilance issues on a small handful of records. Sounds like groove damage.
Yes, sibilance on records is atypical. 
I bought some classical records from a private seller online, all had distortion. It sounded like he played them on an old Victrola.

I’ve gone through this for years, realigning cartridges more times than I can remember. All this to no avail, as it is the pressing as stated. Some older records were played on cheap a$$ players without antiskating, hence it is mostly heard in the left channel as the stylus was digging excessively into that groove wall. It sounds like sssss and often splashes into the left channel. It is annoying as hell, but short of tossing certain records, I just put up with it. I often just buy a replacement record, which often times solves the issue. There are also some poorly pressed brand new records that do this, however the ssssss and splashing is not necessarily in the left channel, just excessive sssss sound.
Classic Records Nora Jones come away with me had this issue on certain songs.
Yes Audioguy85, Back in the 80's commercial pressings were hit and miss but the static and other noise was not associated with peaks in the music. It was random. I had several Columbia discs that actually had little bubbles in the PVC with some of them open to the surface. There was a Warner album with something in the PVC, sounded like sand. I always took them back and got replacements. Sometimes the defect is in the stamper and you get exactly the same noise in every copy you get as the store usually gets a batch of consecutive discs off the same stamper. There was some great music on these labels and like you said, sometimes you just have to live with it....until you get a digital copy of the record:-)