Urgent help - lexus ls400 gearbox issue

[gach2]

Urgently need help

i was trying to refill my ls400 transmission fluid by removing the drain bolt and refilling the fluid.

While doing so the drain nut got stuck and wouldnt come off (like it spun but didnt come off). Started taking the sump off but gave up half way
Anyway after this i went to reverse my car and it wouldnt reverse, it all went foward (dont know if in gear or just lunged - the only gear that walked was park, even in neutral the car went foward, thought this was due to the sump being half removed)

So took it to my mechanic to get the sump removed and remove the bolt and all put back on with new oil and filter etc
and still not much difference still just goes foward, the only difference now is that reverse feel like neutral and rest of the gears are like drive.

my mech says the gbox needs a rebuild

Any ideas why this is happening????

[dnegative]

What oil did you put in?

[gach2]

toyota type 4 atf