I've 10,000+ LPs - but no RCM. Maybe I should have - but..~5mins to
clean each LP....??
For just 50 LPs there's An Alternative.
Ignoring the prospect that your Iso-Alcohol formulations haven't led
to permanent crackles - and assuming that the 70/80s material is 'Pop'
then you could play them WET - the LP side could be re-wetted when
transcribing tracks if the surface dried out.
Although I'd not do the above, it's a safe bet that you'll potentially
get a silent backgound - even more so if you cleaned the LP beforehand
with a water/detergent solution -"Morning Fresh" 'Wildflower
Melody' (Mauve..) is pretty OK - no citric acid, I suspect..rinse
under running lukewarm water (if you're adept you can get an
immediately dry surface using that method..).
Wet-playing is well known to have some advantages - and, for your
application, might well be the answer.