It is quite possible that the vinyl itself is damaged from repeated plays on an improperly aligned phono system. It would not be beyond comprehension that such a system may have been tracking at too high of a force and literally "carved" its' way through the grooves. If that is the case, there is nothing that you can do correct the situation as the vinyl itself is damaged.
Other than that, it sounds as if you purchase lp's that may be in various conditions. You might want to try a trick that Michael Fremer recently investigated and recommends. That is, using a portable hand steamer to loosen the grit followed up by a thorough scrubbing and a rinse.
I also think that Buggtussel's "vinylzyme gold" record cleaner might be worth checking out for such situations. It is enzyme based and may work on some specific "grime" that other alcohol based cleaners can't remove. Sean
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