E-unit cleaning on a GN 3100 Berkshire

I obtained a Lionel Great Norther 3100 Berkshire in excellent condion, but have run into a problem after only a short time of running. It is stuck in the forward direction lucky for me not reverse). I have seen helpful tips and info on here and the internet about cleaning the e-unit, but my problem is I have been unable to tell how to remove the engine boiler to get at the e-unit. Parts diagrams that I have obtained from both Lionel and a K-line maintenance book on Lionel while providing lots of information don’t give me any good idea what parts to remove to get inside to clean the e-unit. I am not knowlegable enough to risk taking the drive train apart, so if that is the solution I will have to send it to a Lionel service center. Any help/suggestions? I have triedseveral tips on cycling the e-unit such as tapping to locomotive, and stopping the engine on the tracks manually (grasping the engine while moving slowly) and nothing has worked.

Look for a screw under the front truck, 2 in the rear and the entire chassis comes out of the shell.

I will have to try that, sounds sensible, will post back when I get a chance to try out the suggestion. Thanks.