I have no experience of the egs gearbox, but the symptoms you describe are exactly that of some of the 'auto adjusting clutches' that Citroen fit

My car has such a clutch - sometimes it'll slip if you accelerate from about 1800rpm in 4th / 5th / 6th, then after a while it no longer slips. It's been doing this on and off for years ! Once the clutch 'auto adjusts' it stops slipping for another few thousand miles

I've found that if I'm a little 'brutal'

with the clutch I can hasten its adjustment
