Rgc, you are certainly NOT left w/ useless LP's, good heavens! I am curious as to the nature/content of the 'grunge' you speak of. Can I assume your mat and records start off clean? If so, then by 'grunge' you must mean some kind of (sticky?) coating that appears on the side of the record that was in contact with the mat, yes?
Some critical thinking is in order ;--) Whatever it is, had to come from the mat or from the record itself. I'm inclined to think that the silicone surface of the mat is somehow 'drawing out' some of the excess mold release agent as it migrates to the surface of the records. Mold release agent is a stearate compound which is mixed with the vinyl before pressing. It flows at a lower temperature than the vinyl, so as the vinyl cools and sets up, the release agent is still in a semi-liquid state, which allows the record to easily separate from the stamper. But then, it too hardens.
It's important (silicone mat or not) to get as much of that agent off the record as possible -- to prevent build-up on your stylus and to prevent dirt/dust from getting imbedded into it over time. I was told all this during a recent conversation with one of the techs at Quality Pressings, a new high tech stamping facility which Chad Kassem recently built.
Removing the mold release agent takes either solvents (like Premier, or Last super record cleaner) to dissolve the release agent enough to then remove it with regular cleaning fluids. If you read this cleaning tutorial from Loricraft http://www.smartdevicesinc.com/Cleaning-tutorial.html
they make it quite clear that record cleaning solutions alone will not work to remove mold release. Steam (heat) is the other option which like Buconero117 is my preference. And you can read why on this thread http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1316435825&openmine&zzNsgarch&4&5#Nsgarch
Unfortunately the thread got hijacked by the "cleaning fluid du jour" crowd ;--) So boring!
Anyway, my guess is that if you get rid of the release agent, you will eliminate the problem. It's certainly worth a try; otherwise, I suggest you call AudioQuest and demand your money back!