I am slowly going about converting my '89 RX from R12 to R134a because the pulley bearing on my original compressor failed. I removed the evaporator today and took it apart to get the expansion valve out. The first thing I noticed was some weird rubber/tar gunk around one connection of the expansion valve and around where a piece of it touches a coolant line. What is this stuff? Is it necessary? I hope it wasn't put on to contain a leak. It wasn't tight on the parts so I don't think it was to fix a leak. The pictures below show what it looked like. I took the pictures after I peeled it off so it is just laying there as a representation in the pics.
The new expansion valve I bought from RockAuto has different thread sizes than the original so it won't fit. It also won't fit over the pipes to seat against the O-ring. I will have to return it. It also has a third connector coming out of the top. I found this thread that says this was a feature of Hitachi A/C systems, but mine is Panasonic.
I was going to get together with a local Subaru group on Saturday to work on this but I don't think I can get a new expansion valve by then. My thought is to use new O-rings and reuse the original expansion valve. It seems people frequently do this when switching to R134a from R12 with no adverse effects and I never noticed anything to think my original had problems.
Thoughts on the weird gunk and reusing the expansion valve?