Yes 5 series e12/8 is a good way too go. All the electronics of the E28 shape in a e12 shape. You do get a 518i injection model 4 cylinder.
Normally look for the fuel flap, if on the driver side then its a later e12 and most should have injection. Very early models had a fuel flap next too the rear numberplate) Most earlier models were carb including the 528 (some with the same twin carb setup as a 530). The 528 was the base for the 530MLE.
Stay away from the 2.0l 4cyl twin carb version (also badged as a 518). Worse BMW i have ever owned, BMW is not known for good 2.0l in 6 cyl format so stay away there too, under powered..
If you can find a nice 528i, 535i or 530MLE (GOODLUCK) then they are the better versions. A good clean 518i with all the extras are also good finds, good reliability, good power for the size coupled with economical fuel consumption. (for the age)
http://www.gumtree.co.za/a-cars-bakkies/lenasia/1984-bmw-5+series-sedan/1001218340150910342403209
http://www.gumtree.co.za/a-cars-bakkies/vereeniging/bmw-e12-528i/1001221050180910029700809
http://www.gumtree.co.za/a-cars-bakkies/bellville/1983-bmw-5+series-sedan/1001220151190910325515209
form the list my personal choices, to go look at. Think Belville is in cape though
Spares are still pretty common, even from after market spares shops like Midas and such.
Door rust a problem, cracked door hinges on front doors. If fitted with a sunroof its a bonus but can lead to rust at front a-pillars, BMW had a strange idea of drain pipes ending just about the bottom of the windscreen and then filled the pockets with sponge for sound proofing, not an ideal situation.
Rust on bottom of windscreen lips also a common problem.
Good luck on finding a nice car and joining the oldies club.