ARC LS15: did they ever use Mundorf MCaps on it ?

Your freight and $ for the checkup easily exceeds the used price of the pre
Mundorf Mcap supreme may not be better than Infinicap type S.
silver gold oil is a different story. Most important is to get rid of the cheap bandaid .01uf bypass cap at the output if ever there's a mod attempt and you are using a premium cap there.

There were two versions of the LS15. The second version had different caps, an improved power supply, and a replaceable power cord. I had my original LS15 upgraded by ARC to the later version, except for the power cord. Don't remember the name of the caps though.

If you go to the ARC Database. The LS15 pictured has Infinicaps.

If you are truly interested in buying this preamp your best solution is to have the seller send it to Audio Research to be checked out. Once Audio Research has given it their approval they can forward the preamp to you after you have paid the seller. I have done this several times with great success. It relieves the seller of liability and the buyer knows he is getting a unit that is working properly.