Yes it is always repairable, nothing special inside, except from the electromechanical stuff (switches and potentiometers like in any old amp but those in the Luxman are sturdy and probably OK) and the main two big capacitors which are nonstandard/no longer available for physical size (read: mounting needs to be adapted), if one would be defective (usually they are still very good).
You will need a tech specialized/experienced into vintage amps and it probably will not be cheap.
In the end, most techs are NOT into fixing stuff existing before they were born, so selecting exchange components not existing anymore is a timeconsuming learning curve.
So repair yes, economical repair probably no.
The L309 has its schematic on the internet, the L309V does not
