I've had both, first and last the SL and used those along side the SL2 which was the first Leica I bought new.
Although the popular thought is the SL2 was the better camera, I like the SL. The SL2 shape change was suppose to make it handle better, I like the SL. The focus screen on the SL2 gives you more 'options' with the split rangefinder style in the center, but darkens with long slower lenses or close-up macro work, the SL is simple and does the job and gives a ground glass look but brighter. The SL2 has a more sensitive meter, good but for handheld work the meter in the SL is good enough.
Both are built like tanks, but the SL2 does have some Japanese parts from the time when Minolta was working with Leitz, the SL is completely Germany engineering/made.
The SL2 is usually going for a few hundred dollars more these days (down from its really premium prices of a few years ago), and you can pick up an SL at bargain prices now - of course the lenses were and still are 'the reason to get a Leicaflex' as they said even back when these camera were new. As mentioned, some of the super-wides don't work on the SL because of mirror clearance, if your are planning on getting one of those the SL2 will be the better choice now rather than 'up-grade' later (or just get an R-series that's working well).
Things to look for; finder problems, yellowing, mirror deterioration, meter is working!, battery compartment corrosion (these take the older PX625 mercury batteries no longer available so an adjustment with the alkaline replacements or other easy solution will be needed, the SL2 takes two batteries), A good CLA should probably be done to start things off right, these are 30+ year old cameras and most of them haven't been used much in the recent past, like the M-series Leicaflexes don't 'sit' well.
