What's your tractor serial number and what are some of the numbers you see on the two-speed components?
4430s were produced for five years and several changes were made.
Assuming there is adequate oil to the two-speed (a big assumption these days) the most likely problem for your complaint is poor sealing of the inner brake piston packing. An improved piston with two oil holes cured this problem.
Unless the 2 iron clutch drum sealing rings have worn badly into the brake housing, the assembly is well worth rebuilding. Don't just take the friction disks out. Tear the whole thing apart and check the planet pinion shafts and bearings. Expect all the bushings and thrust washers to to need replaced, also.
When you get it back together, make sure the tractor will pass system and lube pressure tests with hot oil.