FYI. I read on a different post that this reel cannot be retrofitted with ball bearings vs. bushings. (would be a 6000c). However, I sent mine back to the factory and they can and are doing this. (pre 1,000,000 serial# 1967-1969). They do not recommend for use in saltwater however. Beautiful workhorse of a reel. (Made in Sweden back then).
I believe the issue is the little amount of protection the bearings have from sea water. If you clean the reel thoroughly after every trip it should not be a problem. Most of my Abus have bearings and I've had no problems.