It sounds like a Zinc Chromate type primer. But without pictures that is only a guess. However, if it is the Zinc Chromate primer or some semblance thereof. I would be questioning why the paint is flaking off from the primer. That primer could have been compromised and therefore it too is suspect. I would strip off the paint and see. Either way, you need to thoroughly clean the grease, oils, dirt off before prepping for paint again. That prep includes sanding, fairing, and cleaning. And any bare metal needs either Zinc Chromate priming or an self etching primer applied. Then you go for the paint. But not just any paint. You will need a catalyed paint for it to shine and be hard enough to stay on the outdrive. JMHO