i'm in the same boat as above and op. the skills are versatile and conditionally 'essential'. I had a drastic schedule change that sidelined some of the newer pieces I have been working on w / my teacher and a last minute recital opportunity sprang up, I was given up to a 10 minutes of music window, no way I could learn new or current pieces in enough time to make it so I pulled out a book I worked through about 4 years ago, surprisingly, a lot the ground work was still there so far as musical ideas but the mechanics had to be dug up and re hatched.
I found the above strategies effective. More than anything, I have found that approaching it 'as new' that is, through the learning processes, finding opportunity to find new expressive elements and ways to execute it even better than you did in the past has helped. The 'familiarity' of the piece can be a killer, but trying to find a new 'freshness' to it allowed me to put fourth the effort needed to shore things up. i'm still on the wire on if i will be ready in time or not (i dropped one of the '3' and focused on the better 2 remaining). So it's learning process for me too.
OP, if you focus on how you used to play it you'll frustrate yourself and that has an effect on how you currently play it. Set a goal/deadline and work towards it, use a metronome, etc. Get back to basics, the clean up process should move fast once you put in the necc. ground work, it's a grind, but it's necessary.