Leaky capacitors need replacement?

Which MkII do you have, the fixed bias version (you set the bias) or the cathode bias version (amp sets the bias)? I ask because all fixed bias MkIIs are well over 3 years old (mine is at least 15) to my knowledge. A cathode bias version may be within that time window.

I set the bias.

The guy I bought it from said it was 3 years old.

Looking at how tarnished the solder is, the grey color and cosmetics of the plastic wrap on those caps, and how long they are (much shorter now), and that they’ve already leaked, I’d say more than 3 years old.
Or they were NOS caps of the shelf that were used and not formed, as electrolytics also have a shelf life and need to be re-formed very slowly when new but old.
https://www.youtube.com/watch?v=vA8YksKJSsQ
Boring as bat **** voice on this guy

Cheers George

My gosh, I’m rebuilding 2 amps right now that are 35 and 38 years old, every cap in both amps were in better shape than those. I didn't catch in the thread which amp that you have. I don't think that you'll find most of those caps in what I recommended in the voltages that you'll need. But I would definitely change any caps with the best that I could find and make sure that you get high enough voltage ratings.  Good Luck,  Tim

If it fits check Mouser part # 647-UCS2V330MHD, the difference in size is 16mm diameter versus 12.5mm, but the ripple current is 900mA versus 380mA for the UCY series.