You should be able to get the correct gasket from the flaps, especially if they carry Dorman. I think I have a catalog around here with the correct # for a 235, it might be at the shop. I'll see if I can find it if you want the gasket and/or plug #s.
BTW, you may want to replace the plug at the same time, the threads may be worn/streatched from overtightening by either a po or quick lube place trying to stop a leak rather than replacing the gasket. that can also cause a leak like what you have.
