OP, you're on the right track. Besides penetrating oil and a long lever, you'll need patience.
A while back my bike and the spare bike both had problems one spring and summer. The lead mechanic at my LBS applied penetrating oil daily for two weeks, every other day for a couple more weeks, and finally got it loose after six weeks. A month after I could ride the main bike, the spare bike BB went crunchy. Same rigamarole, except this one only took a month to break loose.
(Teflon plumbers tape FTW! No problem for ME to R&R the BB last year, 10 years on.)