Do you mean a specific manufacturer's brand name, i.e. Micron, Kingston, etc.?

I have a few A1138s, about 6 in total, and whatever make of RAM I have fitted has worked OK. I did have one stick of RAM fail, but that was replaced by the supplier with another stick of the same manufacturer and it works OK now.

I have a few spare sticks, and the names on the chips themselves, in the main, are Hynix, and some are sourced as supplied/labelled from there, and I have a Micron labelled stick of RAM, but I'm sure I have other sticks/chips by other manufacturers and suppliers, so this is not in any way a definitive list of RAM that is compatible with an A1138.

I think any reputable online supplier will swap any defective RAM they might have supplied for a working stick of RAM. At least that is what my supplier did when the one stick they sent me failed soon after I'd fitted it.