How much isopropanol is effective but safe for viny?

Invictus, I don’t necessarily agree with your thesis that 98% isopropyl alcohol would not damage a record even after a prolonged exposure to it. But in practice this would never happen in my house anyway.

Yep, I am sure you do consult the Dick Doctor. 
I've already asked, what are your "facts"?  State your case.  My own "arrogance" is based on trying to find the truth, only.  If I were to find well conducted science that proves your point, I would be more than happy to accept it.  What I have found so far casts doubt on the notion that diluted isopropyl alcohol, used once or twice per LP, could do any possible harm.  I am open to your logical counter-argument, but not your BS.  Have you accepted the fact that cartridges are inherently balanced devices, yet?

I found this, from an article written by a chemist:

"Unfortunately, there are many misconceptions related to plasticizers – for example, about phthalates “leaching out” and “easily dispersing/gassing out” from PVC products. This is actually unlikely to happen unless very abrasive detergents or solvents are used or if the items are exposed to extreme conditions for an exceptionally long time. Plasticizers do not readily migrate or leach into the environment from items because they are physically bound within the PVC matrix. If they could readily migrate, flexible PVC would not remain flexible and perform as intended."

Feel better now?  (Phthalates are one kind of commonly used plasticizer.) The key words are "physically bound within the PVC matrix".

bpoletti, After a search of the scientific literature to support your claim (which I have heard before this) that alcohol removes plasticizers from LPs and could by that mechanism damage them, I found exactly one reference, which is contained in a review article published in 1991.  Unfortunately, I cannot access that article in order to evaluate the evidence for myself.  Can you provide same?

I have a feeling that the plasticizers are associated with the PVC in such a way as to at least inhibit their leaching out by alcohol, and moreover that the cautious use of alcohol at a dilute concentration would be harmless.  (I would not use 98% isopropanol.  No. And I don't wash my LPs more than once or twice, usually right after purchase and maybe once more if there is stubborn surface noise on an LP I otherwise adore.) 

And despite ebm's characteristic declarative single sentence opinion on this subject, I would wager that more than 50% of us use some amount of isopropanol in our RCM concoctions, for good or ill.  There certainly is no profound negative effect.  In US machines where the cleaning fluid is also heated up by the US energy, perhaps the elevated temperatures might enhance any damage that could be done by alcohol.  I really don't know. So maybe I would not use alcohol in my US machine. Anyway, the heat would also drive off the alcohol, lowering its concentration.

I don't remember what it was, but I think there was some question about using Photo-flo for cleaning LPs.  Anyway, something I read did cause me to stop using it about 10 or more years ago, in favor of Tween20 or Triton X100, or even Dawn.

I think I would limit the definition of a surfactant to a substance that reduces the surface tension of a liquid in which it is diluted, in this case of water.  This allows the water to be "wetter", to penetrate better.  Whether this also results in faster drying may be true, but I am not so sure it's a good thing, if so.  If water plus surfactant (usually a nonionic detergent) dries, then it leaves a residue.  In addition to isopropanol, my RCM concoction also includes a few drops of surfactant per gallon or so, and I usually use Tween20 or Triton X100.  (I think Dawn is fine in this application, too.) But I always rinse with pure distilled water to avoid leaving a residue.  My results have been better since I added the distilled water rinse cycle.

I've used up to 25% with no problems ever, in the sense that cleaned LPs sound better, not worse, after exposure to my cleaning concoction.  But I ALWAYS use laboratory grade 98% isopropanol (also known as "isopropyl alcohol") as the basis.  Do not use rubbing alcohol or anything lesser than pure isopropanol.