My front master cylinder is leaking and I'd rather not spend over £300 on a new one if I can avoid it.

Long shot, but has anyone got a used spare sat on their shelf that they'd like to swap for some money? 

Not easy to find one of those. I recently got a stainless sleeve inserted then bored to 19mm or 3/4in And had a piston made then next time its easy because all you need is a seal replacement.  Many clutch and brake repair places can do it, you may need to ask around as some will say no they cant do it. Cost me $200AU and was a lot cheaper than a new OEM if they have them.
This may help
https://www.aliexpress.com/item/1005003064759772.html?spm=a2g0o.productlist.0.0.4e61bacb1RKXUn&algo_pvid=7b3cd171-ed01-492e-b62e-76fcb6d401d0&algo_exp_id=7b3cd171-ed01-492e-b62e-76fcb6d401d0-30&pdp_ext_f=%7B%22sku_id%22%3A%2212000023730995067%22%7D&pdp_npi=2%40dis%21AUD%21%2111.18%21%21%21%21%21%402103255a16576784702596646ea381%2112000023730995067%21sea

Cheers Rick,

Hopefully at the weekend I can find some time and investigate exactly where the leak is coming from so I have a better understanding of what it needs 

Be sure to also replace the external, cylindrical rubber boot on the 16V master cylinder. It deteriorates and often is the "cause" of the internal seal leaking due to debris buildup, as it faces the world's crap in an oncoming rush.

BMW part number 32 72 2 310 756. The 'Bins, Sherlock or others may also stock it in your part of the world. #8 is the one.

It's been my experience with the 20mm M/C version that they're often scored in the bore beyond rebuildability (is that an actual word?!). Even though there's a piston and seal kit readily available. You can see it in the image as #20. But, sometimes we get lucky and you're able to get it to seal...

Two Wheels Better wrote:Be sure to also replace the external, cylindrical rubber boot on the 16V master cylinder. It deteriorates and often is the "cause" of the internal seal leaking due to debris buildup, as it faces the world's crap in an oncoming rush.

BMW part number 32 72 2 310 756. The 'Bins, Sherlock or others may also stock it in your part of the world. #8 is the one.

It's been my experience with the 20mm M/C version that they're often scored in the bore beyond rebuildability (is that an actual word?!). Even though there's a piston and seal kit readily available. You can see it in the image as #20. But, sometimes we get lucky and you're able to get it to seal...

Thanks TWB