If you mean the 4MT tender loco then there is a bracket on the lower right hand side of the cab that the pipework attaches to, the pipework clips into the bracket. You need to separate the pipework from the bracket to remove the body.
There is also the problem of the reversing rod on the left hand side of the loco, it was unclear if this was glued to the body and I cut through it only to find it was a push fit. This needs to be separated from the body as well.
There is more general information in this thread under Train Surgery : Adjusting the pick ups on a 4MT - best way to proceed.
I will watch your thread with interest as my loco is still not 100% right