Many (many) years ago, we had an arrangement of a lorry driver on duty. On one ocassion, the duty driver's services were required (which was rare, mostly the duty drivers were not actually called) and I noticed that he had a strong smell of alcohol on his breath. It was only a very short drive and I said nothing.
A few months later I heard that the same driver while being on duty again, took a scooter for a ride around the car park wearing no crash helmet. The scooter wasn't his, and he was not an experienced rider (though technically his driving license allowed him to ride it). He crashed into one of the parked lorries at speed, and was thrown forward, his head hitting the lorry's front bumber.
He never regained conciousness. He was in Intensive Care for a week before they switched the machines off. I went to see him, his head was swollen and bandaged, and his family around him were absolutely devastated (he was a young lad, in his early twenties).
I never learnt if he was over the limit on that particular day when he took the scooter, but to this day I can't help thinking that he may have been, and that had I said something beforehand he would have been sacked but would still be alive today.
Do what you feel is right....