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

Yet another one of those "minty" condition units.
Tell the seller to take a breath mint.

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.

OP says M-caps not M Supreme if I recall correctly.
As we can see there are several members here who belong to the school of die hard "keep it stock". I respect that but I personally am a "respect the mods as long as its done right (get close up pics), as long as you research the sonic character as the components replaced."

Close up photos will reveal workmanship of the mods.
If lack of reference point (you dont have friends who have a stock/similar unit) and resale value is an issue where you are then stick with a verifiably stock unit.
The LS15 is not that expensive. By the time you send it to Audio Research for check and retube and stuff you might as well pay a premium and buy a stock unit.

Rrog, Do you work for Audio Research or sell their gear? Please kindly reconsider your comment.
You may be stereotyping a whole lot of well respected boutique component manufacturers who work with honest and knowledgeable modders out there.

Good luck with the ls16 bid

HifiGeek, you have all my respect for your knowledge of Audio Research gear. If I recall correctly you are one of their official off-factory repair depots. I sincerely hope you dont view GNSC's cease of operations as a one less competitor. Huntleys mods are expensive. But for many of us it sure beats paying big $$ for trade arounds.

Best of luck to the OP.
If you like the Audio Research sound, not to mention their great support (we here are spoilt by the excellent support from Leonard in the past and now Kalvin), then perhaps saving some $$ and jumping up to the reference series will save a lot of $$ lost in incremental trade ups.
LS22 / LS25 are balanced design. Do you use balanced cables from source to power amp to take advantage of that?
Yes they will work with SE source and power amps connected with RCA but yo uwouldnt be taking advantage of the design.
They are very dynamic sounding but overall not my cup of tea.

Just my own personal un/non-professional opinion but based on my experience with modding a few Audio Research units.
Take out the whole output cap/0.01uF bypass combo, replace with 2.2 or 2.7uF Mundorf Silver Gold Oil or VCap TFTF. No need for 0.01uF bypass. The bypass caps are a bandaid for a less than optimal main output cap.

@Ketchup check out arcdb for the schematics of your line stage. Very easy inexpensive mod. If you put a scope right at the input of the regulator to look at the raw B+ you will see why I recommended a choke.