New Car and New Oil Leak from Taco Plate Options

[nwm5709]

I recently picked up my first 914 - a '74 2.0 with weber carbs. One of the first things I wanted to do was install an oil temp gauge since there wasn't one in the car when I got it. I installed a new temp sender with a new VDO gauge and now I have a pretty steady leak from the taco plate. I actually installed it twice. The first time with everything the same as it was - same O-ring, same bolts with regular washers and no paper gasket. That proved to be a bad idea as it was leaking tremendously. I know that over-torquing these is a common issue, but I honestly don't think I tightened it that much (although I admit I didn't use my torque wrench)

The second time I re-installed it with a new o-ring coated in a permatex sealant, my homemade cork gasket since I couldn't find it anywhere online, and (2) 1/4" lock washers I had available. It is much better, but still leaking a decent amount.

So does anyone have any suggestions? Right now its probably livable, but I would certainly like to fix it and know if I did anything wrong. I don't think I over-tightened it enough to bend the plate, but who knows. I also didn't use the oem crush washer but will that really make a difference?