Glad you can hobble around a bit! at least you can look stuff over and get ideas of the problems!
Unless your cylinder is leaking inside past the piston seals,--the check valve could be sticking open or worn out.
The controls in the bucket could possible not be holding too. My Hi-Ranger has some weird valving on it ! Still trying to figure some of it out too. I am not going up in it unless I have a ground person at the bottom controls! I am not too keen on the idea of going up 70 feet and not be able to come down in a safe manner.
From your tag, I would say model # Tel 29B,and possible T under the dark spot. I would say 29 foot model.
F8627 looks like serial # and 2000 could be working pressure of the hyd. system
5 6 86 could be build date and 300 would be bucket capacity load limit.
Just guessing here! LOL! Keep us posted on your progress!

"A machine you build yourself is a vote for a different way of life. There are things you have to earn with your hands."