I have just had the reservoir to body seals fail from a GRK1035 kit from Mini Sport UK after only two years of use. These parts should last a long time without failure since they don't move (much).
If anyone has a master cylinder like a GMC227 please watch for seal failure. I believe this is due to defective components like usual from Mini Sport UK. They were purchased in 2019, I have since stopped buying from them and probably thrown out all their other stuff. I have no idea if any other supplier uses seals from the same manufacturer, minispares are more expensive so are likely a different (better) manufacturer.
Luckily I noticed it before losing brakes, unfortunately I now have brake fluid all over my engine bay paint.
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