Welcome Alain,
OK, by microphones, I'm assuming you're talking about the pickups. They should be fine, The ones installed are standard Schaller pickups from Germany. I would keep them unless you have a preference for a particular type. Many people use Seymour Duncan Seth Lovers. Bare Knuckles, Throbak, and DiMarzio. You'll want the gold covers to match the rest of the hardware, of course.
It is very possible that the potentiometers have become dirty, but can often be cleaned with some contact cleaner. You might try cleaning them and the testing while they are still out of the guitar. Or, you can replace the pots. Most people like CTS pots, and those are most likely 500K audio taper. You can check them with a VOM.
Heritage used Vishay polyester capacitors, which are good.
The Roy Clark is a very nice guitar. Your H serial number means a 1991 model. It looks to be well care for. Enjoy it!