I have eliminated the heater core bypass system on my 92 RS. This leaves a fitting on the metal heater core return line that runs up the pass. side frame rail that needs to be plugged (3/4"). The cheap fitting caps that you buy in the "Help" bubble packs at the parts store are very low quality. They crack, split, disintegrate and start leaking after only a few months (the fact that the exh header tube runs about 3" from it probably doesn't help).

Does anyone make a coolant line fitting cap in 3/4" size with some quality to it?