Hmmm
Did the guys check the slave cylinder over, or did they just bleed the master. The air has got into the system somehow and chances are, without finding the source, it will do so again - soon !
Mine was fine for a while after having bled it, but the problem quickly reappeared
A tell tale sign is that hydraulic fluid is visible when you remove the slave cylinder. It may be worth a quick look before you set off for a long run