Up untill a month ago, i also used to clean and re-use my filters. After each race meet, i'd open up the engine, clean and inspect and i always had pre-mature wear. I was replacing pistons/sleeves/conrods way too often and that was an expensive excercise on my RB engine!!! I then decided to read the instruction booklet that comes with the engine and i am now getting much less wear and the engine is staying tight for much longer. The booklet quotes

"....Make sure that the foam of the air filter is completely oiled and in perfect shape at all times. Change the foam filter on a regular basis and DO NOT clean and re-use the foam". That is exactly how it is writen.