Thinking about a high ratio transfer myself.......cheaper than an O/D refurb.
You need a definitive diagnosis of whats wrong with yours 1st really but it's a lot quicker to swap boxes than to pull one apart, find out what needs replacing, order the parts, put it back together and re-fit.
Sorry for your troubles mate
Blue beasty.
If I manage to get one and if I get the box sorted I will let you have a drive.
Regards