Most water filters use water at a much lower pressure than the line pressure. Even though the housing is rated for the 125 psi, the cartridge inside is not. It needs to have a lower pressure so it will filter the water at a specific rate. Anything more and it looses its effectiveness. If the regulator is leaking, you can either order a new one from the mfg, or repair the old one. Its probably just a seal or oring thats leaking.