SS vs Poly Tubs
Hoover twin tub washers sold on this side of the pond (and elsewhere for all I know), did not have all one piece stainless tubs. Rather the thing was made of parts (welded?) together, and eventually many probably gave way to leaks. Once this happened the machine had to be scrapped.
My Hoover service and repair manual gives part numbers for the tubs, but highly doubt many if anyone went through the expense and bother of having a new tub put in, unless of course it was a warranty repair.
Hoover advertised the "health" benefits of the poly tubs as being "seamless" with no "cracks, or crevices" for dirt and one assumes "germs" to hide.
Despite showing the breath and width of Hoover's washing machine line, my vintage service manual does not show a single US washer with a heater. This inculdes the early washer with a mounted wringer.
By the time Hoover's washers came along, plumbed hot water was the norm for most all homes. Just as with full sized washers there just wasn't a need seen to have a heating element. Chlorine bleach is what would have been used for whitening, stain removal (whites), and sanitising laundry.