[jeffnc]

I've been using microfiber for almost everything now, especially since I've been finding them pretty cheap. But in the higher nap sizes I haven't tried because I can't usually find them, and it's never a critical application (always a popcorn ceiling or OSB such as your situation.) I'd use a 3/4" nap (maybe even 1") to get into the nooks and crannies, in a cheap version. I wouldn't even consider cleaning it out - I just throw it out.

 

[jeffnc]

It is going to be difficult to get 3/8" into the nooks and crannies of a rough OSB surface. Basically, that's what 3/4" nap was invented for.

 

[jeffnc]

I don't even use 3/8 on smooth walls 1/2 is about the smallest regular naps I use.

Why is that just out of curiosity? I find the 1/2" leaves too much texture sometimes.