Rob Clarke

Hi I know nothing about engines, engineering, gearboxes and the like. My sincere apologies. I have a narrowboat with, I'm told, a Lister LH150 Hydraulic Reverse gearbox. Having made it through the Standedge Tunnel, it started to cut out when I put it into reverse. Initially it would restart and move into reverse okay, but it became progressively worse on the downhill stretch to Huddersfield, and since getting to Mirfield I was unable to get it into Reverse at all, it's permanently stuck in forward gear. I've got it down to a wharf in Wakefield and they've checked it over, but it's nothing particularly obvious (adjustment etc) so I need advice from an expert - is it fixable? Am I looking at getting it taken off and sent away somewhere? New gearbox time? Help! Thanks Rob