When the lid on my AR-12 tumbler wore out, I made a new one from some plexiglass (and ordered another on the web). The first lid wore thru in 7 weeks - the plexiglass lid lasted almost 10 weeks. The only down time in either period was to wash the barrel and change grit. It is fascinating to be able to watch the grinding motion as the tumbler barrel rotates. It is even more fascinating that the plexiglass "fogged" a bit as I used coarse grit for grinding but polished back to sparkling clarity as I moved to finer and finer grits and finally a polish run.
A lot of glop - but not in the motor, not in the bearings.
The clastic sediment is an amazing material. It flows rather easily in some circumstances - as in the photos. At other times, it is sticky and handles much like a plastic - even feels like a gooey plastic. The flows in these photos look subtantial enough to bear some load but, in fact, the ooze was very loose and that on the wooden platform was watery.
I'll get this all cleaned up and from now on, new lids every 6 weeks. Period.
If you would like to read more on clastic rock, start at Wikipedia.