Winter is hard on mountain bikes. The wet and grit cause lots of wear of all moving parts. The transmission is especially vulnerable but suspension bushes can also suffer badly. Ideally you wouldn’t want to put your best bike or bikes through this and classic mountain bikes are even more prone to wear from muddy conditions than modern. If at all possible you should try to have a winter bike and accept the inevitable degradation. I have a 2015 vintage Trek Fuel EX8 full suspension bike to use until next spring, if it can survive that long. It’s starting to look rather out of date in the rapidly developing world of MTB with its steep steering head angle and high bottom bracket. It also has only 120mm of suspension travel at each end which is less than I would expect on a more recent offering. It’s still a good ride and with the softer ground in winter the suspension will be adequate. The jockey wheels on the rear mech. are very worn and I think this explains the poor gear change. It has a wide range 1 X 10 setup so there’s less to go wrong than with its original 3 X 10.
Today I was excited to ride a 29″ wheel bike for the first time since spring and took it to Healey Nab to compare it to my Boardman FS Pro, which is also looking a little dated. The grip immediately seemed superior to the Boardman. You get more tread in contact with the ground with the bigger wheels and it shows. It climbed better over slippery obstacles and felt to have more in reserve around the corners. Another advantage is that the wheels ride more smoothly over bumps and dips. On one particularly cut up section the difference was very noticeable.
I rode for 3 enjoyable laps and my conclusion, despite a reluctant gear change, was that 29″ wheels are the future. I simply wouldn’t spend my money on anything else. Yes, I’d like a more modern bike, with greater suspension travel, but I still had an excellent ride on the old boy.