Honda HP400 product Carrier

There wasn't a category for this oddbal piece of equipment,so I thought I'd start here.I picked this Honda HP400 product carrier which while it has many uses,it's designed for masonry work.It is fully tracked,has a dumping container & fits thru a 32" doorway.My problem is with the drive clutches.It has one lever on each handlebar & drives like a bulldozer.It has a 3-speed transmission ,but the clutch is internal to the engine crankcase.Actuating the levers to disengage the clutches does steer it but won't disengage the power to the tranny.I found the owners manual online & the lever/cable adjustments are correct.The end of the cables go to a lever on the crankcase [ like a motorcycle ] & the lever has full movement. None of the local dealers have ever seen or worked on one. It is operable,but putting it in either the 2 fwd. or 1 Rev. gears obviously grinds when you shift it & makes using it a bit precarious.I'd appreciate any idea's on what might be wrong or where I can find info on it.The internet hasn't turned up anything but an operating manual which has basic adjustment & troubleshooting.Just not my problem. Thank You , Sgt.Rudz .