Update, since adding dr tranny all was well.. Then i took my 2.5 tonne van for a spin. The car developed a transmission fault( like rich's) no gear change down from 6th.
Reset a few times and got home with limited gears.
Drained the oil when home, replaced with fuchs 4400 .
Box is now smooth as butter, towed van upto the high country, no problems at all. No shudder, no fault.
It seems adding mr tranny can cause transmission error, i guess the oil was so knackered the mr tranny thinned it too much.
Thanks to "koos best" for the fuchs 4400 tip.

