I have not used MKS pedals in quite a while, but all free bearing pedals are similarly serviced. I did have a pair of MKS on a bike for about 25 years. They were still spinning smoothly when I sold the bike.
When I have one of our bikes with serviceable pedals up on the stand for maintenance, I'll check the pedals. The best way that I found is to remove the pedals from the cranks, and spin the axle by hand. If I feel any roughness, it is time to repack and adjust the bearings. I do the same for sealed bearing pedals. Unfortunately, It is usually pedal replacement time when sealed bearing (Look pedals) feel rough. When getting ready for a tour, I'll service the pedals as part of my pre-tour maintenance. That usually means the pedals on our touring bikes get serviced once or twice a year. We have completed 2 tours this summer ( about 1000 miles), and are leaving in a couple of weeks for another 6 weeks. I'm not messing with them for this upcoming tour. That would be overkill. However, I'll still pull them off and check them for smoothness.
Last edited by Doug64; 08-16-12 at 11:22 PM.