What should I look for when I take the motor apart again. It occassionaly slips out of second gear, when very hot. I have already replaced all 3 shifting forks. Nothing in the motor looked damaged last time apart. A thousand degree turbo exhaust housing sitting 6-8 inches above the tranny might need to be heat shielded. The heat radiates onto the engine cases.

 

Next time apart.......
You need look for worn or rounded dogs,they should have a small 45 degree chamfer,but the corners should sharp...not round and shiny.
This requires all the gears to be taken off the shaft,for observation.
If you look at the tranny pic below...you need to check the dogs between gear #14 & #16 those are 2nd & 5th on the secondary shaft
exploded tranny view
If a bent fork was not replaced in time,it will still pop out of gear.
Good Luck
Jeff

 

I have never seen a DS tranny apart, but if it is like any other manual tranny and the forks are ok then it could be the dogs on the gears like Jeff mentioned. If these dogs are worn and rounded then chances are the hub that engages/synchronizes the gear is shot also. Does the DS tranny have blocker rings and syncros?? If so, inspect them as well.