Only Cub Cadets - Got a free rzt42 zero turn

Hello all, new to the page. So I like to work and rebuild things. Have rebuilt boats, jetskis, cars and now my first mower. This one has been sitting for a while and I got it for free. Owner said he went to use it at the beginning of the season and it wouldn't fire, so he ordered a Deer. So got it home and found the starter was toast, got a new one, carb definitely needs a rebuild/replace, new battery, new blades, new tires. So questions, the right hydrostatic drive is frozen. Tried using the release levers and the left rolls fine but the right is locked in. Had to use a winch to drag it on my trailer. I know both drives have been rebuilt (both have black RTV on the sealing surface). What should I do to get this wheel free rolling? I did get my new starter in today and test fired the engine using my jump box and starting fluid. It fired up and ran with me spraying fluid in the carb. Valves definitely need adjusting and the valve cover showes signs of oil leaking. So that's where I'm currently at. Really need to figure out this drive issue.