How much does the Repair Arm augment repair?

Solution 1:

From personal experience (which seems backed up by this thread where the developer responded), the Repair Arm heals you 1 hull point, regardless of the amount of scrap collected.

From the developer via that thread as well:

We didn't want it to be always a positive, obvious choice. The power of constant repairs after every fight is too useful without at least a few setbacks. [...] I might sell it come sector 6 or 7 if I'm doing well since that 15% starts to hurt a lot more and the extra boost to finish off the boss is helpful.

The FTL Wikia seems to agree with this as well:

Repairs your hull by 1 point every time you collect scrap[.]

Solution 2:

Currently Wikia states "1-2 points", although I'm playing with it right now and it seems like 2 points happens most of the time (on normal).