Hi. I've treated some 1700-1800 LP's with LAST since about 1980, and think it is an excellent preservative, particularly if your vinyl gets a lot of play. As you may be aware, the abbreviation "LAST" stands for "liquid archival sound treatment". The chemical composition of LAST is intended to reduce the effects of wear by the stylus, apparently by bonding to the vinyl molecules. LAST is used by the Library of Congress to help preserve old recordings, which is a pretty good endorsement for the product's safety.
The purpose of LAST is not to make the recording sound better, except to the extent that it reduces wear in the LP's grooves. However, based solely on my own listening impressions, I think that LAST does make a slight but audible improvement in the overall sound, perhaps due to reducing the friction between the stylus and the LP.
In short, I think LAST is a good investment if you have a large LP collection that you want to preserve, or simply if you have some prized and irreplaceable LP's that get frequent use. I have only one caveat: make sure your LP's have been thoroughly cleaned before using LAST -- which you evidently have been doing.
