I've shot with a fair amount of Contax cameras over the years. I've never had a 139 though, so I can't speak to anything about it other than the well-known issue with the body covering (looks awful, but it's a relatively easy/cheap fix if you want the camera). In the past I've had a pair of 167mt bodies, and an RX. Currently I have an RTS III, which was a camera I could only dream about at the time they were new. It is a big, heavy camera (relatively speaking) with a 6 AA battery power supply. The reasons to want it even in spite of the weight are the capabilities of the camera (1/8000 top shutter speed, 1/250th top flash sync, the vacuum film plane which holds the negative flat against the pressure plate at the moment of exposure, 5 fps motor drive, and the quirkiest of its features - the otf ttl flash metering for non-dedicated flash units). It also has some great ergonomic features - a 100% viewfinder, and (IMHO) perhaps the smoothest, silkiest shutter release action of any film camera I've used.
If you are still considering the system, another camera you might want to look at is the 167mt - it's smaller and lighter than the RTS, and it is one of the newer bodies in the lineup ( the RX is newer, but it is bigger/heavier than the 167). The 167 had one particular feature that was groundbreaking- it was the first camera to feature auto-bracketing. The weak point (again, imho) is the batteries - by default it uses AAA batteries, if I recall correctly. That saves on weight and bulk, but they don't last as long. There is a battery booster grip for it that replaces the bottom plate and lets you use AA batteries, at the cost of some size and weight. Also, the 167 was the first body in their lineup to take advantage of the MM mount (which stands for multi-mode) - MM lenses will let you shoot not only in aperture priority, but also shutter priority and full-auto program modes - earlier bodies don't have a program mode, so do not require MM lenses. The non- MM lenses are sold as AE lenses. When you look for them, you'll see the lenses marketed as MMJ (J stands for Japan), AEJ, or AEG (Germany). I think there may be MMG lenses but if they exist they are very uncommon. Some people put higher value on the AEG lenses just because the glass was made in Germany. I do not know that in the real world of usage it makes any difference. Just be aware of it from a pricing perspective. AEG lenses are more likely to be older than J lenses of either variety.
Another body you might look at is the S2/S2b. No motor drive to add weight, more compact like your Olympus.
The reason above all to get into the Contax lineup is the glass. They made some phenomenal glass, and unless you have to have the super fast versions of their lenses, they're still very affordable compared to the Leica equivalents. Last year I picked up a 300mm f4 telephoto to use mostly adapted on my Fuji XT2 for doing wildlife shots. I wanted something inexpensive because I don't do that much wildlife shooting, and the Fuji native lens that would be close to it was almost $2k. I got the Contax lens plus a 2x teleconverter and a trio of macro extension tubes for under $500. Recently I got a 100mm f3.5 for doing casual portraits for $200-ish. If you want the fast 100 f2, that will still set you back over $600. Same deal with the 85 2.8 vs the 1.4. The 2.8 is $200-ish, the 1.4 will run you over $600 for one in good condition.
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