low gear stalling

I brought a used MINI Mini 1.4 (75bhp) First Hatchback 3d 1397cc (2009) about 6 months ago. It has about 75000 mileage. For the last 3 months we have the following symptoms after an oil overfill (I know, it was stupid): - Low gear stalling (normally on first gear but very occasionally at 2nd)...