Hi Sulzer,
Hope this helps, this is the way I tackle it myself.
Remove the cab at the front end first, that is the opposite end to the roof grill. Remember to just unclip the handrails from the cab or you will break them off, it just slips out of the little hole at the corner of the cab side window. Most people recommend removing all the handrails first but I found them a nightmare to put back on, so this is a way around that.
The cab should just pull straight up but you may need to use a very small flat screwdriver to ease it away. What I do then is turn the loco upside down and if you turn the bogies to the side you will be able to see the small tabs which hold the body on. They will easy to spot if the loco is in an orange livery! You can then use the small screwdriver to help release the tabs, the body plus the cab at the grill end will then lift straight up. (Remember to unclip the handrails from the grill-end cab as well before removing the body!)
I find his much easier than trying to squeeze the body sides to get it to unclip, as you said you seem to need to use a lot of force to move it!