William:
According to Parts Lookup (above), if it is a Hydrostatic, its a 383. It also looks like for several assemblies the Serial Number break is important. Do you know your Serial Number?
The PTO appears to be common to both. Judging from the assembly depicted on Parts Lookup, I would be looking at all the pulleys, their bearings, the linkages, etc to be sure that I have all the parts and that they are assembled correctly with as little play as possible. Problem could be in the deck itself, the spindle bearings and/or the pulleys. I would especially pay attention to how Arm Assembly (Item 13 [10?]) engages the Idler pulley (Item 11).
382 Gear & 383 Hydro, 134-382-399, 382 Gear, 134-382-100, 383 Hydro, 132-382-399, 133-382-100, 133-382-399, 132-382-100, 0350032U, 0350028U, 0350029U, 0350033U, 0350036U, 0350037U, 132-383-100, 133-383-100, 134-383-100
PTO Parts List
Tag . . Part # . . . . Description
1 . . . 703-0292 . . . Arm Assy, Shifter
2 . . . 703-0293 . . . Lever Assy, Shifter Arm
3 . . . 732-3019 . . . Spring, Extension
4 . . . 720-3006 . . . Grip, Shifter Arm
5 . . . 703-0296 . . . Rod Assy, Mower Clutch
. . . . 714-0474 . . . Cotter Pin
. . . . 736-0140 . . . Washer, .406 X .812 X .051
6 . . . 703-0297 . . . Actuator Assy, IPTO
7 . . . 738-3017 . . . Bolt, Shoulder IPTO
. . . . 712-3009 . . . Hex Lock Nut, 5/16-18
8 . . . 732-3021 . . . Spring, IPTO
9 . . . 747-3034 . . . Rod, IPTO Return
. . . . 714-0474 . . . Cotter Pin
. . . . 736-3030 . . . Washer, .469 X 1.469 X .090
11 . . 756-3013 . . . PULLEY-IDLER
. . . . 712-0375 . . . Nut, 3/8 Cad P/T Lock Type 1
. . . . IH-21742-R1 . Washer, 1.031 X 1.500 X .027
12 . . 703-0295 . . . Bracket, Cont
. . . . 736-0463 . . . Washer, .281 X .625 X .051
. . . . 712-3006 . . . Nut, 1/4 Type 5
13 . . 703-0299 . . . Arm Assy, IPTO Idler
. . . . 736-3032 . . . Washer, .406 X 1.000 X .056
. . . . 736-0169 . . . Washer, 3/8 Lock