cleaning gritty surface noise on LPs

Back in the '70s I used a Disc Preener to clean my records.  At times I, or perhaps a roommate, might have gotten the Disc Preener too moist, and the result has been a low-level, gritty surface noise on some of those old records that are otherwise in good shape.

I've tried cleaning them with various record cleaning solutions (mostly alcohol-based) with my Nitty Gritty RCM, and nothing has lessened this particular noise, even though they have worked fine with other LPs.

Has anyone encountered this problem and solved it?