A slow puncture is probably the result of picking up a nail. If you know you've got a problem go along to your local tyre fitter and get it checked out very quickly and often free. Don't take a chance on adding to statistics.
I had a rear tyre with deep tread delaminate at 70 which was a bit scary - luckily it was on the rear. It was some polish brand tyre which was on the car when I got it. Dont take any chances for the sake of a 15 quid puncture repair.