I ran into the same problem with my '49 3100 when I got it. It had sat in a shed for close to 30 years. I ended up jacking the rear wheels off the ground. Then I took the shifter arms off the side of the transmission. Then take out the bolts that hold the side cover on and gently pry it loose from the transmission case. When you start to pull it off take a light and look into the transmission and make sure that the shifter forks are coming out of the transmission and staying put in the side cover. Then I pulled the drain plug out on the transmission and put a drain pan under it and got a can of penetrating oil out and started spraying the sliders and gears inside the transmission. You should be able to use a pry bar and carefully turn the transmission some. Don't get to carried away and if it doesn't turn on the easy side spray it some more and let it sit for a bit. You don't want to start breaking off teeth on the gears. It took me a few days before I got mine all freed up. You can go to Keith Hardys site and get a look at the shop manual. It will identify all the parts inside the transmission for you and also show you how to position the shifter forks in the side cover for reassembly. Good Luck Don
