Again 1972 never recapped. Only tubes replaced. It is possible depending on use, environment, and some luck.
Common in the 80's. 50 yrs later not so much. Sitting for decades never being used is the worse thing for old Marshalls.
Electrolytics go bad. Just a fact of life. So do ceramic disc, tubes, PCB's and about everything else on the planet.
I heard all kinds of bullshit cliches when taking 3 years to decide to mod my JMP in 2011. I still hear them. Was also at the height of "Kameron amp snatching season".
Just forum opines. To thine own self be true.
What a boring musical world it would be if no tube amp was ever "modded".
I have a friend of 50 years that swears to this day that a 1979 JMP 2204 i had was "the worlds most perfect amp".
I beg to differ, i needed 50 more watts, an 2 more gain stages and an FX loop.
Again, mearly opinions.
And 9 outta 10 60's / 70's Marshalls floating around on ebay or reverb or CL are beat to shit and going to have a host or problems only a 50 yr old
amp can have.
As for this 23 minute video above 20 minutes of it he's talking. He doesn't play a note until after 8 minute in.
Kinda hard to gauge that.