The radiator is one of those areas where Aprilia seems to have cut a few corners. But something worth noting is that the bikes will go a very long way with little or no fluid.
This has been tested (mainly by) Dobbi in such places as Morocco, and most of the UK. Also by YTC1 in such places as Mongolia and Russia.
The radiator fins are easily damaged, but can be repaired with our old friend epoxy resin (for small leaks). Otherwise it is possible to get the core repaired. East End Radiators will do a check and repair service by post.
Adding a Radiator Stone Guard is highly recommended.
The fixing of the radiator overly hang it from the two fixings at the top rather than seat it on the fixing below it. This causes a telltale breaking of a core at the rear of the radiator close to the upper fixing point near to the expansion tank. This Aprilia Forum post shows what usually happens.
Many reports that adding a thick washer underneath the bottom fixing point pushes the rad up enough to stop these stresses passing through the cores.
However, if you have a hole, aluminium brazing is unlikely to work as it is so thin it melts so easy and the rad holds so much microscopic dirt heat applied tends to flash and bang.
The best way to do it is to open up the broken core with a screwdriver and stuff it full of chemical metal, epoxy resin then build it up around the fault to ensure it can't expand and contract to continue the crack further down the core. It will look messy but done well it will be entirely permanent.
One or two missing cores will not cause the cooling system to run any warmer.