I have been wondering this for a while too. Somewhere I read Adam Drake and on the RB engine website said not to reuse the foams, just get new ones. However, Ive been cleaning with motor spray/nitro cleaner then with dish soap and they are fine.
On a side note, with the Losi preoiled foam filters, what air filter oil do they use? I have Traxxas now, but when I clean the blue stuff out, then put the red traxxas oil in, it looks kinda weird and I dont think it is good for the air filter. I havent ran those yet. Im assuming Dynamite air fitler oil?