The brake compensator valves are fitted on a lot of light commercial vans, and some cars too, they are a common fail point, but sometimes you can get them working with a lot of working the mechanism and oiling, at the end of the day all the unit does is restrick the flow of brake fluid to the rear axle reducing the ability to lock up the wheels on heavy braking when unladen
You could get one of these and retro fit it into the vehicle, they all do the same job, at different pressures
If it was not there at all, it has been known to pass the mot, like a lot of things like this
A last resort would be remove it fit a standard brake pipe system, mot at another test station (seen this done a few times)
As you would not probably be putting it through the heavy strain loaded like it would have been in service this would suffice
Not actually worked on 101s very much, although driven a few, I know they are a heavy drive, especially the hard top version
