[limey]

I can't really help you with re-acquiring your old pieces - but any and all playing should help to get these back "into your fingers" again. My problem is that if I play my old repertoire, I play it with my old, bad habits all intact. For me it's better to work on less familiar stuff.
Playing music with other people is a whole new ball game. If you're used to just playing by yourself you may well have got into the habit of stopping every time you make a mistake, or just playing at a very variable tempo (speed) which suits your interpretation of the music. For the first problem - you'll just have to work at not stopping if things go wrong, but try to keep the flow and rhythm going and get back into the piece as and when you can. For the second problem, depending on the piece, if you feel the tempo should be varied then you'll have to learn to use your body to give an indication of the tempo and/or tempo changes to the other musician(s). Eye contact with the others is good, and rocking or swaying in the new tempo until everyone's got it are basically what's required. And listen to the other player(s) - if you're playing with a flautist they will naturally "phrase" their tunes with a slight gap at the end of a phrase before the next one starts so that they can breathe. You will have to be sympathetic to that, listen for it, watch them and take off together with them into the next phrase.
As to scales, I had an "Ah hah!" moment when I realised that I don't have to do them from memory, reading them is just as good for the muscle memory and that's what I am (and you are) trying to develop. Memorising them was for exams, and I'm not going to take another music practical exam, thanks.
Hope this helps.