Fork cap rusted, stuck.

[hoosierrick]

I was planning on changing the fork oil, but the right cap (spring retainer) had water standing on top of it when I got the bike, and is horribly stuck. I kept pb blaster in there for a long time without success . I am currently soaking it with MMO.
I have two questions.
Can I just remove the air valve and refill with 12 oz of oil through there?
Can I use motor oil,(if so what weight?) or do I need special fork oil?
I want to use engine oil if I can, in case they leak.
If it works out I will get the rt side cap unstuck this winter.

[hoosierrick]

I have been looking on other sites, and I am going to put atf in the forks for now, and see if I can get this thing on the road before the season is done.

[BenInPA]

Rick I am not 100% on it but I believe you do need fork oil. Your local dealer should have some. I purchased a bottle under $10 when I did my fork seals. I personally wouldn't use anything but fork oil in them.

Sent from my DROID4 using proboards

[hoosierrick]

Update; I have been keeping pb blaster and Marvel Mystery oil on top of the cap for some time. I tapped on it with a hammer and socket tonight, and it actually moved. It did not return, it just stayed down, but making progress. I probably will need a new retainer, but I have not tried to remove it yet. I figure I would screw something into the air valve hole to slide hammer it apart. Starting to look like it is not going to be roadworthy this season.
It is starting and running pretty good. Been riding it around the yard because it is not licensed or insured.