Well start by taking the bottom screws out n loooking inside there as you cock it. You might get lucky n solve your problem right there... although I think the non-lever side panel has to come off. That has another light sheild plate inside n a couple light seals that will need to be replaced as they hardly ever get done n will definately get ruined once you open it. So buy an assorted sheet seal kit now from Microtools. It has 5 self stick sheets of the various thickness foam you can cut with a razor knife. You'll have enough to do all the seals on your camera n several backs n the rest of your town's cameras for the wooping price of $25. Also get a nice set of Whia screw drivers so you will have no issues with junk drivers stripping the screws. A small set will cost you $15 or so. The #000 n #00 crosspoint are the most popular sizes we'll need. No special tools are needed to do the job.
Before you get started, you need a well lit clean area to work. I like to have a piece of excersise mat under the camera, screws don't bounce or roll off n you won't scratch the camera body. Get a weekly pill organiser to put your screws in as you take em out in the order of operation. You'll find some screws are longer or slightly different n have to be put back in the same place they came from. Take pictures as well so you have some reference to go back on.
Send me an e-mail, I can detail the steps to get the side panel off, it is a bit lenghty for a post but in reality doing it is very easy.
Your interlocks may not be your problem. It sounds like a bent linkage or a simple adjustment. The only way to find out is to take a look inside.
BTW where are you located?