There is no pin lock on this machine.
I have this SAME model (it was 1 year old when I got it and it was in pristine condition - there was still paint on the bottom of the skid shoes). It works great for me. I got it because I didn’t want to deal with the auto-turn nightmares at that time. A couple of suggestions:
1. Squeeze-handle under left grip.
Yes, it controls the differential that engages/disengages power to the left wheel (there is ALWAYS power to the right wheel). When it is engaged, there is power to both wheels. When you squeeze it, it disengages so the left wheel turns freely with no power to the left wheel. Only squeeze the handle if you want to make a wide turn to the RIGHT or to turn the machine to the RIGHT 180 degrees. Be sure to keep the handle squeezed the entire time you are turning the machine until you want power to BOTH wheels, then release the handle.
2. TIP: After releasing the handle, make sure you have power to the left wheel. If no power, squeeze and release the handle a couple of times. I find that many times, if I squeeze/release several times, that it will engage. Or while manually pulling the machine backwards alternating side to side while squeezing/releasing the handle will get the differential to engage.
3. Don’t get discouraged because I mainly use the feature going in/out of the garage. On snow covered pavement, the machine will often slide enough that you don’t need to use it.
4. Take the belly pan off and tip the machine up into the service position to watch the differential in action. Each time you squeeze the handle, you should see the notches of the differential open and advance.
5. Lubrcating auger/shaft. There are 2 grease fittings. Remove the 2 shear pins before attempting to lubricate. You don’t do anything to the housing attachments. When the pins have been removed, you should be able to freely spin each side of the auger. If one or both sides won’t spin, it’s probably rusted to the shaft because of failure to grease. If ok, attach a grease gun to each fitting (zerk), inject grease and spin each side of auger to distribute until you see grease come out the holes for the shear pin or at the housing. Repeat the process with the other fitting. Then re-install shear pins.
6. BEST advice ever. Use ONLY non-ethanol fuel. I also add Stabil Marine and Sea Foam. Keep this combination in the tank the entire year. After using, turn the fuel shut-off to OFF and let the engine run until it dies. Here is where you can find non-ethanol fuel in your area:
https://www.pure-gas.org
Good luck.
Where are you located? You might want to add that to your profile.