Installed a new Corbin seat and it is too heavy for the installed seat strut. The seat will not stay up without some other support. Anyone have the same problem? Anyone have a source for another strut that can support the added weight? Of course I am assuming the installed strut is good, just not designed for the heavier seat. The Corbin also has the backrest that makes it even heavier. But the seat will not stay up without the backrest either.