1) If it's the chain driving the wheel axle type, check chain tension - it might be slipping/jumping if very lose. Easy to adjust, the drive is mounted in slots and you just drop it down until chain is tensioned and do the bolts back up. Might be the bolts are just loosened.
2) Yep, had that exact same. Stripped the compass, lubricated the gimbal needle bearings and it never did it again. Might also be magnetic interference though, so check with the hand-bearing compass that you do not have any interference around the fluxgate compass first - as that's quicker than stripping it down!
3) Stiff steering might be anything. Helps to disconnect steering cables and see if it's the rudder (bearings are common, search forum) or the wheel/cable part. Use emergency tiller to check rudder resistance while cables are disconnected.
4) It's normal for camping gaz bottles to leak a bit as the valve is being screwed in the bottle. Should stop when it's tightened down though. Also the valve should be closed when swapping bottles. The original regulator is definitely due for a replacement though!
SVB has the one that fits the locker _and_ has a pressure gauge which doubles as leak tester.