You can do more work on the glider than what is listed as "owner approved preventive maintenance", review what part 43 refers to as "major modification". Just remember that what ever you do needs to be acceptible to the A&P that is going to sign off the next condition inspection. He is certifying that the glider is still in conformance with the TCDS as it was imported. I would suggest you use DG parts as much as possible, if you feel a different filter is better, does not restrict flow you can say it is a suitable replacement. But be sure your A&P agrees. Be sure any work you do is in accordance with accepted practices in Part 43. Get the maintenance manuals, referring to them is more acceptable to the A&P and the FAA. Use aircraft approved hardware, if a bolt needs to be replaced, use an aircraft bolt, not an Ace Hardware special. Use approved aircraft wiring, not lamp cord.

Make good friends with an A&P knowledgable in gliders and Rotax engines, make sure he knows what you do, see advice. The glider will maintain value, shoddy work or obvious non approved parts will make the entire glider suspect at resale and decrease its value.

BT