Our chummy box does this on holiday too. Most strange, but perfectly liveable with. Every year, in France for the last 10 years or so I have had to top it up. I assume it's a combination of ambient temperature and the fact that the dream holiday for 3 speed boxes is a daily oil change, gearbox equivalent of a spa break I guess. Once the last top up at the end of the trip is done it lasts all year, with plenty of use, until the second or third day in the dordogne 11 1/2 months later! Who can blame it?
Have fun, W

Yeah I tend to drink a lot in France, too.

Very reassuring on both counts - merci!