Big vintage amps worth paying for and keeping for a long time

Lamm hybrids, Rowland 8t, Levinson 23.5 etc. How reliable are they and how expensive to fix if something goes wrong ? Capacitors, resistors needing replacement, after 25 years, 30 years, something else ?
I didn't mention Gryphon and Nagra, as examples, they are too expensive even old.