backup Leica reflex camera

[pgs@pa.dec.com (Patrick Sobalvarro)]

I usually shoot slide film and I often notice that I have it in my
camera when I see something that I want to capture on black and white
or color negative film.  So I've been thinking of buying a second body
to take along sometimes with my R6.2.  I want it to be reasonably
cheap: less than $600.  I'm not particularly interested in
autoexposure, but I want a working meter.

So I've noticed that R3's are very cheap, like $300-400 in "like-new"
condition; R4's are only a little more, and the R4S and R4S Mod P
(R4s2 in Europe) often more than $600 in good shape.  I've heard that
the R4 had problems, and also that they weren't all fixed by the R4S,
but the R4S Mod P is supposed to be okay.  This is out of McBroom's
Bluebook, so I'd like to hear some confirmation (or contradiction).

So here are some questions:
1) Can R3's still be repaired if the electronics fail?  (Are parts
   still available from Leica?)  Anybody who's used one of these have
   good or bad things to say about them?
2) Can R4's still be repaired?  Did Leica ever do a "silent recall" on
   these (e.g., an upgrade, as often happened with other models)?  Bad
   experiences?  How about the R4S? 
3) How about the Leicaflex SL?  These are available for a reasonable
   price: $300 - $450.  Would this be likely to be a more reliable
   camera than an R3 or R4?  Will they accomodate a 3-cam 28/2.8
   Elmarit-R?  (I'm pretty confident that they'll take my other
   lenses).

Thanks for any info you can provide.

-Patrick Sobalvarro