Help with Randall RB-120 hiss and static problem

[Liquid Smoke]

Hi everybody! I'm new on this board but I could use some help...My friend has a Randall, RB-120, 1x15 combo, bass amp, 1976 vintage. It's been a great practice amp but it's recently developed a hiss/static (all the time) and fizzy/farty distortion (when playing notes). The hiss sort of goes away for a second when a note is played and it fizzes and farts as the note decays...then the hiss comes back. It's definitely more of a hiss/static that gets worse the longer the amp is on...it's not really what I would call a hum.

What do you think is the source of this noisy, static, hiss, fart??? Based on the sound, if it was a tube amp, I would suspect a bad tube or socket. Does this sound like a bad cap, power transistor, etc. The speaker is ok!

It has two, can type capacitors, one of them is leaking black goo. They are similar to the type I have seen in my Champ but I don't think they are "multi-section". There are only two wire connections. The specs. printed on the cans are:
4-46 FIL-CAP
4500MFD 50WVDC
46075338
The caps are 3" long x 1 and 5/16"dia. clamp mounted.

I can't find a schematic online. Does anybody have any idea what I can use as cap replacement? Or any other trouble shooting ideas?
Speaker is ok!
Thanks

[J M Fahey]

It's very probably oscillating, because of bad filter caps.
You don't hear the oscillation itself but its byproducts, as hiss.
Anyway, any goo-leaking cap *has* to be replaced.
You need two 4700uFx50V caps.
Mind you, modern ones will be *much* smaller, won't fit those clamps, but you'll certainly find a way.
If trouble remains, *somewhere* I have that schematic or a very similar one, close enough for service.
Good luck.

[Liquid Smoke]

Thanks JM,
I've been having a hard time finding replacement cap cans that will fit.
It seems most of them are actually longer than the originals (3") or larger dia. (1.375") and I don't have much extra room to work with.

Any recommendations of where to shop?
So far I've checked Tedss, Mouser, AES, etc.

Thanks for your help!