Bemble may be by but you can search his posts as RRPhil also as that is him on other sites and i have posted a link below to him on another site checking the shift motor resistance.
There are plenty of others on here with more experience than me and i am only quoting snippets of information i have picked up from Bemble and the likes of SaintV8 also.
If the motor has oil in it i would imagine that would cause your problem and if the fault clears with the borrowed motor then that would be your cause but investigate the leak or you may kill a new one potentially if it's not an internal seal in the motor.
Does the transfer shift between high and low ?
The slipping clutch could be the lock up clutch on its way which can be fatal for the transmission as the metal debris finds it's way into the transmission. i understand the valve block is the cause of the TC failure due to reduced pressure on the plates and so by replacing the clutch the root cause hasn't been cured so the problem returns only quicker the second time which could be why your transmission was replaced already at the usual 100k mark and then you are due a second one if the cause was the valve block the first time around.
i believe the test to see if the lock up clutch is working is to drive at 60 mph plus and take your foot off the accelerator and if the revs drop then you are not locked.
Along with the two bolts, was there any metallic debris on the magnets ?
Do you get any rumble noise when slowly accelerating ?
It could also be the 5th transmission clutch failing i guess but hopefully somebody with more knowledge than me will be along soon as i have only worked on one ZF5HP24 transmission.
http://forum.landrovernet.com/showthread.php/208328-Trans-failsafe-prog