Automatic gearbox sludge

[JD-JAG66]

I installed the engine and automatic gearbox from an XJ6 S3. Drove the car a first time for 20 metres (in and out of the garage) before changing the gearbox oil. No problem.
Changed the gearbox oil and filter (cleaning the sump, removed oil was a bit dark, no sludge) and when I tried to drive the car again it would hardly move. Revved it hard but it barely moved. Up to a point where it just spit out the oil from the filler tube covering the engine bay in gearbox oil. Not one of my best moments.
Drained the remaining oil, removed the sump and this is what I found. Sludge. No idea where it came from.
Hard to remove since there was so much of it.


Another image from the filter.



Question.
Has anybody seen this before?
Where could it come from?
The sump is now clean but how can i be sure that all of it is removed from the gearbox itself?
Is there a gearbox flushing / cleaning method that removes everything...Or am I looking at a gearbox overhaul...
Not a great fan of having to remove the gearbox to be honest.

Looking forward to any feedback
Jan

[mgcjag]

Hi Jan....have a look here...you do have a torque convertor that's full of oil... http://forum.etypeuk.com/viewtopic.php?f=5&t=6252

[JD-JAG66]

Ok, update. Flushed the oil by detaching the hose going to the radiator.
Used 14 litres of oil, could have done with less, but continued until very clean oil came out again.
Have the car on car stands so shifted throught the gears as recommended. Checked fluid level when engine was hot, and all seemed perfect.
Unfortunately the gears "selected" but the wheels only turned for a second or so. And then, no matter how much I revved, they would not move.
Browsing the internet I read somewhere that this could be because the sludge would have blocked a solenoid or valve in a open/closed position, but the flush should have removed all the filth.
Any suggestions?