Back from the dead with some $0.02 worth....
I'm on the second set of lower seals (hence second shifter since it is not replaceable) for the T56 Magnum shifter after having made a simple modification that helped a bunch to stop leakage.
The lower seal cracked like every other one I've seen after having been run for a while. However, upon inspection of the new parts the boot is way over stretched to fit on the shifter shaft. This excessive hoop stress in the boot caused it to fail prematurely. The fix? Machine the shifter shaft to accept the boot bore with a more reasonable fit.
After three years the lower boot is still in good shape but a small amount of liquid still ended up above the lower boot but not leaking out of the top boot. With the shifter being rear mounted / not above the gear, I'm attributing this to a possible overpressure condition within the gearcase. So, two things to do: 1) Apply sealant to the bore of the boot and a small bead around the lower edge of the seal-to-shaft interface, and 2) Figure out how best to monitor the gearcase pressure. The as-supplied vent is not kinked, restricted, etc. A better venting system may be needed if on-track pressures are found to rise above atmospheric.
Has anyone tried the Bowler shifter with the Viper lower section?