Nitro can break down into an acid which will etch the engine parts and the methanol attracts water.

Nitro only breaks down to an acid when burned, however it forms nitric acid which is a very unstable rocket fuel, this then burns with the methanol. So it is not much of a problem. However pure nitromethane is a very mild acid itself, but not as strong as vinegar or lemon juice. About a PH of around 6.7 I think. IMO a non-issue, unless you are a speed racer running 70% nitro. Even then only the cylinder and exhaust stack are exposed to any significant amount of nitric acid.