1993 c4 poor brake pedal.! Master cylinder?

Hi
Poor brake pedal
This happened after taking it for tracking it came out of bay with pedal very spongy , felt nearly to floor and hard to stop,it pumped back up on way home but not as it was before I drove there !
Still stopped thankfully, just a bit/ lot more pedal pressure .
No leaks under car or on callipers.
After searching I found fluid on the pressure switch under the master cylinder.

Any advice on what the cause/ problem may be if not a faulty master cylinder, which in that case ,,,,

Has anyone got a brake master cylinder they would like to sell or know where I can get a brake master cylinder for
1993 c4 auto .
Or maybe where to get it rebuilt.

Rockauto list some but all non abs and info on the description very sketchy at best.
Tried email them but no joy keep getting referred back to help section on site .
The ones i have found that might be ok out of stock.

As far as I can tell it's,
5/16 bore
m12 pressure switch
M12 rear brake line
M10 front brake line
ABS line out reservoir
2 bolts to brake booster
Thanks
John

If the fluid you see is very small amount I would not think that is the problem
Maybe sensor threads just need some Teflon tape used

If brake performance degrades only when racing and getting hot you first might to look at
the brake hoses from the calipers to the brake lines
As those hoses get too old and are hot they tend to instead handling the pressure to bloating/expanding
and lower fluid pressure
See if they feel too soft and if so replace them before replacing the master and fully flush the brake fluid
with brake fluid that is made for race conditions