I have a GI .22 conversion kit. Its purpose was for training, and it is OK for that purpose, and is fairly accurate, but I don't think of it as a substitute for a good .22 rifle. I have not experienced any leading of the port or gas system, and I would think that any crud that did get into the port would be blown out by the first 5.56mm round fired afterwards.
(The .22 conversion, of course, is straight blowback and the gas system of the AR-15/M16 is not functional.)
Jim