Given the age, I'd opt to clean them with D (red), then apply G (gold) to protect them. BTW, forget the precious metal bit, it's the color of the liquid, and is meant for any metal. As per which way to buy it, that really depends on the devices (*).
Personally, I opt for 100% liquid in bottles vs. spray cans or wipes. More cost effective that way IME (a tiny amount goes a long way). For a particularly nasty switch or pot, you can use a cheaper contact cleaner first, then apply Deoxit red (D100 or D5 if you prefer/require a spray can) followed by Gold, Shield, or Fader (whichever is most appropriate). Using liquid may mean tearing down switches & pots to access them.
Various lint free swabs, brushes, and wipes are extremely handy with liquid applications, if not necessary (tiny dab on them & scrub surface; repeat until the swabs/cloths, ... come off clean).
The following two documents might be of some help:
Both links are direct .pdf downloads.
* I would think those in the Hitachi would need little to zero teardown to access contact surfaces, and pots can be disassembled if you're careful.