Having owned Thumblers Tumblers for years (I now use the big Raytech
units from Rio) I am somewhat familiar with them.
The bowl is mounted to the central shaft on top of a large washer
held in place by bolts and lock washers.
If by an O-ring you mean the rubberized gasket that keeps moisture
from exliting the the bowl where it mounts on to the shaft, this is
not difficult to remedy.
If the old O-ring has become damaged, or has corroded away, go to the
local hardware store and find a huge washer (large enough to hold the
bowl on). If the inside diameter hole is too big, no worries. Just
find a sturtdy second smaller washer that fits the inside diamter
hole, but overlaps nicely onto the larger diameter washer, center the
smaller diameter washer onto the larger diameter washer, apply Handy
Flux, and silver solder them together.
To provide a seal, get some old rubber gloves and cut gaskets from
the widest portion. The hole in the center should be about 1/2 the
diameter of the center shaft of the tumbler. Use several layers
between your newly fashioned washer and the bowl to provide a good
seal. Cut new gaskets and replace as necessary.
I like to use wing nuts with lock washers instead of bolts to tighten
the bowl down on the tumber base.
You can also 'soup up' your Thumblers Tumbler' by adjusting the
counterweight on the bottom. The motor wears out faster, but
depending on the load and media, it can reduce cycle times.
M. M. Rogers Design