Exhaust valve fouling buildup

That's a lot of build up, but you do have 2K hours. If they are exhaust valves then the heads need to come off and sent it to be pulled apart and completely cleaned. Other areas may need to be checked too as this may not be the only area of with deposits.

What type of fuel and oil do you use and what rpm do you cruise at? If you use 100LL do you use a lead scavenger like Decalin?

? they are exhaust valves. Bought this off of a flight school sling, sight unseen.(likely a poor decision) To my knowledge, they used unleaded. Not sure on oil. It was on the coast. No corrosion, but maybe the salt is related.

What you see is a normal amount of carbon lead buildup for a "high-time" (almost 2000hrs) engine running 100LL Av-Gas. Do a leak-down (Differential compression) test to see if the lead is affecting the piston rings and holding open any valves. You may also want to send the reduction gearbox to an authorized Rotax service center for inspection, as the lead can affect the internal clutch and its slipping torque.

https://dealerlocator.flyrotax.com/

https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/298-gearbox184

https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/181-diff

Wonderful information, thank you. I cannot fathom why they used 100LL...

Pistons and valves can be serviced and carbon build up can be removed. I would send the heads to a service center to have the heads done. They may need to clean out the valve guides and associated parts. The pistons heads can be cleaned too.