The return spring sounds poxed, but is easy to change. The selector cables are straight forward enough, though you'll need a second pair of hands to hold the gear stick steady while adjusting them. Try this:
Take out the air cleaner box, remove the bolt on the drivers side of the engine fusebox, release the two clips on the other end and roll the fusebox forward.
Directly below will be the two selector cables.
The one with the white end is forward/back and the black end is left/right.
The cable ends are adjustable. My issue was with the forward/back motion (white) sometimes I'd have to give an extra shove forwards to get first.
The idea is that you push the orange button in all the way until it clicks into it's housing, you can then slide the cable in/out a litte.
You need an assistant to move things forward/back for a bit to make sure you have it right in your head. I needed to shorten the cable.
The orange button was stuck on mine but a quick squeeze of some pipe pliers freed it off.
I put the car into second, then I pushed in the button and she moved the lever forward (or maybe backwards, I cant remember) with the clip open the cable moves but not the head. she moved the lever very slowly and when it had shortened by two notches I released the clip and it locked.
Took it for a quick spin round the yard and it was perfect. it might take some trial and error, I think I just got lucky.