[TEAM THREE WHEE]

If it is a casting leak due to a crack, then the wheels needs to be properly cleaned, and welded, then dressed off and re-chromated. If the leaking is due to porosity in the casting then the process id different. For slow leakage find a company that specializes in casting impregnation. The wheel would need to be cleaned with and acid bath, rehromated , then impregnated, but check with the impregnation company as they may impregnate before the chromate.
When we were still sand casting wheels we would impregnate castings after polishing to stop porisity leaks. The sealer was clear and you could not tell it had been done. the wheel was cleaned and placed into a sealed tank. Next a high vacuum was pulled, and the sealer was then introduced, after which it was pressurized . After a time the sealer was drained and the wheel removed.
If the wheel has a crack anywhere in the center disc of the wheel , please replace the wheel and do not weld on the spoke section for safety reasons.
we currently make one-off cast and forged magnesium wheel for vintage race cars.
scott