Harman-Kardon Citation System, 1978

I've been enjoying this system for about 4 years now but the left channel popped a couple months ago. It consists of:

Citation Sixteen A Amp
Citation Seventeen Pre-amp w/EQ
Citation Seventeen Tuner
H-K factory rack. Needs veneer work. Cage is fine.
The physical condition of the components...8.5 of 10.

I feel it's worth repairing but I'm not sure how far to go before I'm in too deep.There is also some crosstalk in the pre-amp but none if there's no other active input, of course. I see a couple ads for upgrades between 4and 5 hundred dollars but that doesn't include repair. I pushed Thiel 3.6CS's with it for a while but now I'm back to KEF 104/2's.