Well, after finding out the most likely cause for my weird slayer problem is a cracked piston skirt, I looked into getting a big block for my slayer. I read that a O.S .21M will fit into a slayer (or revo) without any mods, but is the O.S .21M any good? What is the pros. and cons. of getting it? But, the O.S .21M costs over $250 new. Is that incorrect, or is there some where I can get one cheaper? (I hope not ebay, I've gotten burned on ebay deals) Or, is there any other big blocks that will fit without mods or changes that cost under $150? Any help would be nice! Thanks! -Wolfslash16