[hypoxia]

I replaced the seal in the Headhunter Mach 5 which should resolve the seal sticking problem.  I removed the 12VDC pump along with the associated plumbing.  The backflow valve to the 12VDC pump was stuck open, I removed it and plugged the hole.  There is enough room to reposition the Mach 5 and I added a Grundfos Scala2 120VAC water pump beside it.  The Scala2 will hold a constant 55 psi during a flush unlike the Mach 5 that will go down to around 40 psi before cycling.  I used it for a week & couldn't tell any real difference between the two pumps.  I do not plan to have both connected to the plumbing, I'll have the piping set up to where I can connect one or the other.  Chances of actually needing a backup are fairly small.

Historically, the Scala2 has been problematic with seal leaks, Grundfos has been addressing the issue with design changes, hopefully this late version is resolved.  It has a 3 year warranty.  Parts are readily available.  Home Depot Scala2  FWIW, I purchased through the  Military Exchange Home Depot storefront, 10% off & no sales tax = less than One Newell Unit.