I have an RTS still with the original cover in very good condition.
It's quite a heavy camera and very similar to the Yashica FR1. I think the main difference was the lack of a viewfinder cover.
I have an FR1 too!
The RTS II is a major upgrade from the original. Mine still has its original cover too, also in very good condition.
My favourite Contax is the 139, quite a bit lighter than the RTS series, and with the 2.8 45 Tessar it is almost pocketable.
In fact it is slightly smaller than the G series rangefinders that everyone raves about. (I have a couple of 139s... )
The 137s had an integral winder powered by 4 AA batteries, which also powered the camera functions. I have a couple of both versions-
the 137 MD which was aperture priority and the later 137 MA with which you could alter the shutter for manual operation.
All my 137s, 139s and Yashica have needed replacement leather and light seals.
The Yashica ML lenses were pretty good, just not as good as the Carl Zeiss lenses. The difference in size is quite marked too.
Contax RTS by Ken Dunton, on Flickr
Contax Zeiss 135 2.8 and Yashica ML 135 2.8 by Ken Dunton, on Flickr
Contax Zeiss 200 3.5 and Yashica ML 200 4 by Ken Dunton, on Flickr
RTS II by Ken Dunton, on Flickr
Contax Yashica 004 by Ken Dunton, on Flickr
Contax 011e by Ken Dunton, on Flickr
Contax 139 by Ken Dunton, on Flickr