Brake failure?

[taylormj4]

Checking fluids in the engine bay yesterday I noticed paint on the inner wing around the master cylinder has gone all wrinkly and bubbled up. It looks like brake fluid has for some reason flooded out of the master cylinder lid. I checked the level in the master and it seems normal.

Then on the way to work this morning, had to brake hard at a junction and felt like I only had partial braking force, meaning I couldn't quite stop at the give way line.

Immediately following that, I found a safe area and made some brake tests and found that I now had full braking force.

Are these two occurences linked ?

[taylormj4]

Good thinking, yes that could push the fluid out but no, no new pads. It hasn't had a service for around a year.

Can heat in the engine bay cause the brake fluid to expand so much that it comes out of the master cylinder ?

[taylormj4]

Thanks all for the replies.
It's only around a year since the last service when I presume they would change the brake fluid. Correct ?