I cant say much about the full kits since I haven't seen many of those but I have a STACK of proof that a K & N drop in filter will toast a stroker turbo. The saved for show head count is 8 wheels (not all the ones we've pulled) then one goodish one strung on a rope hanging over my front counter. Its not dusting its chunking! they look like you threw gravel thru the compressor. Not your everyday worn down blades

 

Easy way to see if it has a leak as far as air is concerned is to pop the hood and put your hand around the seals and stuff, if you feel air coming through, there is the leak.

If it sounds like a kenneybell, its possible the bearing is going out. Take one of those long metal hearing thingy doohickies and put it wear the bearing would be on the turbo and see if you hear it making a scratchy or grinding sound, if so, time for a turbo rebuild.

 

Why not spray soapy water on it? If there is a leak it bubbles. Easy and keeps your hands out of harms way