Are you planning to finally check those valves on your trusty Suzuki DR250 or DR350?
 
It's an excellent time to check on your valve cover seals and replace them every 12,000 km or 7500 miles. You'll need a pair of factory O-rings ahead of time.
 
They're located on the engine head, subject to high temperatures, and have a short life span.
 
They will flatten over time and lose their elasticity, and eventually leak. You'll start to see dust sticking around the covers when they're about to fail.
 
This is a Suzuki Genuine Parts:
11177-14D01-000 O RING, INSPECTION CAP