LandPride Razor Parking brake stuck?

Hello all,

My neighbor has a LandPride Accu-Z Razor Z52. The left drive wheel is stuck. I can hear the hydrostat engaging, but the wheel won't budge. I released the bypass valve rods per the owner's manual. The right wheel releases but not the left.

My guess is the parking brake is jammed "on" or there is a solenoid which won't release it. Any thoughts before I tear into this thing?

Thanks for any help...