I haven't participated in the thread before, but I have been using MO and petrolatum in my hair for years without problems.
I have tried other types of oils but always ran into problems. The ones that are light enough to not cause problems with my eczema aren't heavy enough for my hair. MO and petrolatum I've never had a problem with.

I can't honestly say I can remember any build up. I'll keep a closer eye on it for a while to see.
Very fine, high porosity, currently dyed and growing out the relaxed portions. I'm pretty sure my hair's 3b something IIRC. We will be finding out for sure as time goes by.