If you are reliant on a local shop, find out what they service first.
There are a few Mfg's that will not support their older lineup (eg Oceanic, Tusa)
Mfg that support older models:
Aqualung (+US Divers)
Scubapro
Sherwood
Mares (no Dacor support)
Of course there are caveats to this, but overall their support is there. Service Kits are readily available. Some parts maybe not so much.
In addition to a regular service, you may need hoses. This is where it adds up fast lol. Bubble in a compass. Fogged out SPG.
I made a killing not too long ago with this stuff lol.
Your shop, I hope, would go over this with you when you drop them off for service. The set does not need to be disassembled to see where the money is.
Having said that, I would still buy used. Rarely pay what they ask for. I bought 2 complete sets of MkII/190 for $120 not too long ago. Before that an AL Legend set for $60.