Can you buy these separately from a whole cylinder as my passenger rear must have died this morning seeing my brakes sh#t themselves when I tried to slow down on the freeway and i saw some steam coming from the passenger rear. Lost a lot of pressure but managed to come to a stop

I drove the rest of the way nice and slow and will have to park it this weekend unless you can buy the seals from supercheap or autobarn or something

Yes you can, Supercheap and co can get them but I doubt anywhere keeps them on the shelf.

Entire cylinders are pretty cheap so depending on the age of yours its pretty economical just to get whole new ones.

Havent checked if mine are original or not but dont people say the new ones arent as good as the originals

Any decent brake shop or a Mini place should have these seals in stock.
Most Supercrap stores these days don't know what a Mini is.

Measure the piston diameter, or take a piston with you as a sample.
Most cylinders fitted to Oz Minis are 3/4" diameter, except Cooper S or others with disc front brakes- these use 5/8" ones to prevent locking up during heavy braking.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Be sure to check the condition of the cylinder before you go fitting new seals. Look for any pitting, scoring, rough spots etc.