Vintage Tube amp worries

I am looking at a used set of tube amps. They are a little beat up cosmetically and need new tubes. They have not been played in 5 years. They are very highly regarded amps however.
Is this bad for the caps and boards in an amp that's 12 years old but been in storage for 5yrs to just sit unused?
When long in storage electrolyte in electrolytic caps eats out dielectric (aluminum oxide) lowering breakdown voltage.  Presence of voltage rebuilds dielectric.  Power amps thru variable power transformer starting with 50% and increase voltage to 100% over at least one day.  I'm not sure if low voltage can do any harm to tubes.
What brand are the amps?
5 years not powered up doesn't sound like that long. As mentioned I believe it depends on the brand and quality of components used. I have seen older tube amps sit for 10-15 years and then plug right into the wall (no variac) and power-up with no problems.
The amps are VAC.
Thank you to all who post and your expertise.