Going out on a limb here to see if this idea might help the OP, without him having to go drilling in there.
Get a can of brake cleaner, one with the fine tube for attaching to the nozzle and insert that into the lock, to help contain the spray within the lock. COVER any painted surfaces above and below the triple tree where brake cleaner could run/splash out. (Hoping it will run out somewhere, of course.)
You have put oil in there already, which is bad for locks to begin with, as it just attracts dirt. Powdered graphite is what you want to lube locks with.
If that works to flush out any crud, the brake cleaner will eventually evaporate with no residue and it may free up the lock. If so, once a day or so has passed, lube with some graphite.
Good luck with whatever route you have to take to correct the issue.