The seals for the Tina and T10 are TC 20 x 35 x 7
There are two types – Nitrile and Viton (Viton being much more expensive)
There are two sub types – R21 and R23.
They both have a single sealing lip but the R23 has an extra dust lip to avoid grit getting onto the sealing lip.
Here is where I got mine:
The item was £1.20 but the postage was nearly £7 which makes it quite and expensive one off order!!