you must've heard from the wrong street

engine is in, new exhaust and gauges are done, we're just stuck on a leaking water (thermostat) bypass-pipe.

i made a 'custom' one up off the car, but now that the engine and shiz are in it isn't working so great, it leaks from the top. can someone conclusively say if the O-rings do the sealing, or if it is the top of the bypass pipes that do the sealing?