One thing to learn is that leakage refers to electrical leakage, not goo oozing out. If you do see goo oozing out, then, yes, the part is bad. But you cannot tell an electrically leaky cap by looking. You would use a voltmeter or a cap tester.
Do they sound great? Maybe stop fixing them then.
If originalness is important to you, then that is my approach. If you want relatively reliable service for regular use, then maybe more preventative replacement of components is called for.
When you replaced "all" the electrolytics, do you mean just the main filter caps, or are you including the little ones that bypass cathodes and such too?
Certainly at 40-50 years old, any electrolytic in there is suspect. Your film caps could be fine, or they could all be living on borrowed time... and not making the payments.
And original or not, tone is a matter of the whole thing together. PArt of the tone you like mght even be the fact that some parts are leaky. Put new parts in there and they might be "better" parts, but you may not like the sound as well. Shiny new stiff shoes may not be as comfortable as your old running shoes.