I would think all ability stats grow with each amount of EXP you gain, as with all other sailors, but a small percentage of not much is not much.

e.g my Kaiser B.O with proper experts and vets only gives 6 repair 0 overheat at lvl 120, I'm sure it was probably +8 or +9 base stat for repair.

This figure would be even more miserable with stripped B.O's for SS etc (obviously)

At the end of the day i don't think its that much to even be considered given a decent Repair Man.

Just my opinion, someone with greater knowledge may be able to enlighten us further.

The repair ABILITY of a lvl 120 BO is lots of orders of magnitudes greater than that of a lvl 12 BO. True repair ability of a lvl 120 BO shows an even greater difference.

The repair stat GROWTH however ( how much ability you get with each lvl you gain) is exactly the same ( given the same statring repair stat).

Yes it does, every time your BO level up you can see your grow and ability

My RN Lvl120 BO (100 vet, 500 exp) alone gives 31 DP/S repair rate.

So yes BO's repair ability grows when leveled up.