I agree that you should leave the original three in one capacitor can in place and fit replacements (if necessary) under the chassis.
I think you should definitely NOT attempt to re-stuff the original capacitor can!
For cheapness you could just buy one single 47uf @ 400 volts working replacement capacitor and fit it in place of each of the three in turn and see if it's just one that's causing the problem, starting with the one nearest the rectifier which is the reservoir.
You say you couldn't find replacements - there must be dozens of places selli theradial type.
Cricklewoods in London do a 47uf @ I think 450 volts with good ripple current rating for a couple or three quid - plus the dreaded postage of course. Phone them with your bank card details and order one if you don't do Paypal.
Just found the Cricklewood capacitor, link below:-
https://www.cricklewoodelectronics.com/47A450.html
If you do replacements under the chassis, you could just fit them roughly for a start to see if it cures the fault and if it does, you can then decide to make a better job of fitting them later. If it makes no difference, then just connect back up to the original can and look elsewhere.