Okay..... UPDATE!
SO.... I put this nefarious little ba$t@rd to one side awhile ago, did two other double ended 930's with comparative ease.
The other day, I decided to go back to this nefarious so and so and have another go. As per a previous post, It seems that indeed glue was the culprit. I slide a thin blade between the chassis and the end of the loco. This seemed to give a bit of give. Eventually, POP off came the body and at long last, I could do my decoder installation. The problem was with a brass etch at the rear for what is probably to represent the coupler levers. The person assembling the loco was VERY generous with their use of glue!

So as far as instructions for dismantling...
1) You do NOT need to remove the staff exchanger. The body/chassis will move past the staff exchanger casting. YES this IS contrary to popular belief. (side note: On my first 930, I removed the staff exchanger box, but in subsequent (four), I haven't with no issues) The cab interior "may" come out, but no issue.
2) The rear handrails do need to be disconnected from the body. This seems to be better than removing from the rear steps, though this may be six of one, half a dozen of the other. I found the handrails rather painful to re-install. I ended up letting the holes out a little with a 0.5mm drill.
3) I used the cast "tank" to hold the chassis with neddle nose pliers, while "flexing" the body. This worked really well.
4) While the chassis/body will separate around the staff exchanger, once dismantled, I altered the cab a little. Firstly, I cut off a little bit of "dash board" and ensured that the fireman and the headlight casting didn't foul the exchanger. You can't see this alteration. when re-assembled.
5) If there seems to be something stuck, then slide a thin blade between the body and chassis. I also used small pieces of card (like a business card thickness) to assist separating the body from the chassis. There are four lumps that "hold" the body on. Slide the card over these lumps to "release" the body.
These are my thoughts. Assuming that glue hasn't been splashed around, this loco is not that hard to dismantle, but it is fiddly. The conventional wisdom of removing the staff exchanger box is **incorrect** which is a prime finding. BUT having removed the body, life is easier if you alter the cab to facilitate easier replacement.
I really do not see why dismantling a loco should EVER be this hard!!!! The issue did seem to be the metal etch at the rear. It was glued to the Chassis? and excess glue then attached the body to the chassis. So now I've been able to dismantle the loco and install a fantastic Loksound ESU decoder!
Cheers! and Happy Australia Day!!!