The oil seals in the gearbox are standard-type oil seals for rotary shafts and can be found for a steal on evilBay if you search for the size (i.e. 30x45x7). That #14 is a unique size, though. May have to go + or - 1mm in thickness to find one. Do some research or just get them all at Aftershock. Likely to be discontinued at the dealership, but maybe worth a try. Some dealers have new old stock (NOS) and also have knowledge of part cross-ref in Suzuki, Yamaha, Kawasaki, etc parts.
Factory seal info?
#13 Oil Seal 30x45x7 91261-ME4-003 $6.33 (factory price)
#14 Oil Seal 35x57x9 91223-VM0-004 $7.95 (factory price)
#15 Oil Seal 30x52x9 91224-VM0-003 $6.40 (factory price)
And yes the oil seals get replaced from the outside. Once you have a replacement seal there on your bench, THEN remove the old one. Take a small screw and screw it a couple threads into the old seal. Then pull the screw/seal combo out with some pliers held onto the screw. Don't try to use the shaft or housing as leverage because you can scar the sealing surface and/or crack a case if you try too hard. They usually come out with just a little effort though.
The shocks have a few notches on one end for pre-load adjustment. Check to see both shocks are in the same notch. If you're going to spend the big $'s on Works shocks, might as well put some limiting straps on the trailing arms (to frame), too, so you don't snap a pricey shock if/when you snap an axle (or vice versa).
In addition to a compression check, make sure you do a leakdown check for air leaks. #1 killer of any 2-stroke is lean failure.