all i can say is good luck with finding the 4700uf 120v low ESR caps for a reasonable price. that is one of the many reasons that i do not like to take LT550's in for repair, along with many other brands of older amps. i am going through the same obsolete parts issue with older Bash amps.
you can go with a higher voltage cap though. like say... 160v.
there may be other issues then just the caps.
one thing i noticed with some of the amps, is that they used some kind of brown glue to hold parts in place. pry/cut the plastic cover on top off and make sure that it is the capacitor that is leaking the electrolytic, and not just a sloppy glue job. but with the age of the amp, it would not surprise me if the caps are bad.
i do have used 4700uf 120v caps that test good if you cannot find any new replacements.