Im pretty sure my oil switch is leaking, theres oil everywhere around it and my oil light keeps coming on, id say repco would not stock them, do any companys make them for the 18RG?
i say tell your oil warning light to take a hike, just go out buy yourself an oil preassure guage which will go straight into where the excisting oil light sensor is and that way you fix your leak problem while also being able to monitor what your engine is doing.
I am thinking that is a fairly standard item. They are a standard thread I think, and many different pressure switches will fit. Repco will have one I'm sure.