I believe they changed the sender after series one, but I can only find one (later) type in parts listings and on ebay.

Mine appears to be leaking oil and I want to put a new one in,and it has been reading very high lately as well.

I wonder if there would any issues other than perhaps a slightly different reading on the guage, with a later sender?

They are cheap enough, give it a whirl. It can't damage the gauge.