In terms of reliablity the SL, R6.2, R6, R7 and R8 are probably your best bet. Personally I have the SL, R6.2 and R8 (and Nikon F3-P).
With the SL you will probably experience 'operator failure', before the camera gives in. I have one and it literally feels like it was milled from a solid block of brass. It's the most solid camera I've ever handled. Supposedly Leica lost money on every body they sold.
In operation it feels like a Leica M, with a reflex viewfinder, which is amazingly brilliant. Supposedly the shutter is very accurate in terms of speeds. It sounds like a cross between a Leica M and SLR.
There are a few R lenses that the SL can't take, because of issues with mirror cleanrance, but it's a very small number (check the internet). The SL2 will take all R lenses, but the 1/2000th speed can be unreliable. Other than that it's a great camera.
The SL meter takes the old Mercury type batteries so you would need to have it recalibrated (match needle display).
The R6.2 is pretty close to perfect. It's no bigger than an M body and very, very well built. The viewfinder is extremely bright. Metering system is very accurate and offers spot and average modes. Supposedly the shutter is very accurate in terms of speeds. Reliability seems to be very high. Mine has never given me a problem. Salgado shoots with these and they seem to be working out for him. Apparently the reason why this camera went away, was because Minolta could no longer cast the body shells for Leica. Other than that the guts are Leica and a Seiko shutter built to Leica spec & design. Believe it or not, Seiko makes extremely reliable shutters.
The R7 is about the size of the R6.2, but packed with automation. I've heard a lot of good things about this camera and they demand a pretty high price as far as R bodies go.
People seem to have a love hate relationship with the R8/R9. Some people call it the 'Hunchback of Solms'; others an ergonomic masterpiece. I'm in the second camp. IMO the controls are placed perfectly and better than in any other SLR I know of. My biggest complaint is that it uses an odd CR type battery, that isn't as widely available as AA. If you get the Winder, also get the rechageable battery pack. Otherwise you may end up in the poorhouse, as you burn through expensive CR batteries. Due to it's unorthodox design it draws attention, when you carry it around town. The R8 was a new design, from scratch by Solms and had no Minolta content. It's all Leica.
But other than that the R8/R9 a brilliant camera and apparently very reliable. I tend to meter 95% of the time with a handheld meter, so the R8 is a little overkill for me and I may sell mine down the road.
The R4 and R5 are older models with the highest Minolta content. They certainly are reliable for cosumer use, but from what I have heard they can't really stand up to a professional pounding.
The R3 looks interesting and comes from an era when most things were built to standards that today would be considered very high. Leica saw the R3 as a pro-camera and were quite proud of it, but I don't have enough experience with this body to form a clear opinion. It is based on a Minolta design, but keep in mind that is was a few decades ago, when Minolta actually was a competitor to Canon and Nikon...
I'm surprised that your F3's are giving you trouble. As you know they have a reputation for being close to indestructable. Have you considered having them rebuilt by Nikon? I'm sending my F3-P's in shortly. They are such nice cameras and I've sort of fallen for the old scalloped Nikkor 2/50-H.C, etc
HL