The whole service recall thing is a preventative practice by BMW. They are fitting a one way rubber valve because the pressure in the shaft tunnel is apparently pushing off the rear rubber cover and allowing water into the tunnel, which could impact the shaft. The test they are doing is to put a measuring disc on the rear after taking the wheel off, then seeing if there is a vibration. If the bike fails this test, the shaft is replaced regardless of any inspection (replaced by exactly the same shaft with no modifications to it). BMW have started the campaign with GS and GSA, but other bikes use the same shaft and bevel box including RTs. We have had shafts replaced on RTps and normal spec RTs, including 2020 and 2021 bikes with less than 10k on the clock. But one RTp has over 61k miles and the shaft was changed, but it hadn't failed. There is nothing about shafts have to be changed at 36k, if the bike passed the test, the shaft will not get changed, even our 61k RTp had to have the test done, so it wasn't an auto shaft replacement. So will the rubber one way valve stop corrosion on the splines - possibly, but as I stated earlier, there is no modification to the shafts being replaced, so there is nothing that has been "fixed" or modified to the design. For most I would think that they will never have an issue with the shafts.