In my first job as an apprentice motor mechanic at a small garage when I was about 18 I was often the last one in the shop and entrusted with locking up and waiting for customers to collect their cars. Late one afternoon I was alone again but waiting for a lady in her 40s who said she would be coming after work to pick up her car, which was already paid for.
Since she took a bit longer to show up than I expected, I washed my hands but kept my overalls on in case I needed to show her anything. On impulse I opened the glovebox and found a clean pair of her panties which she must have put in there but forgotten about. They were made of white cotton and I began to get an erection as soon as I sniffed them, even though they had been washed. Since I was wearing underpants with a fly in front, I let my penis poke out through it, though it was well hidden by my overalls. I quickly put her panties back before they got dirty but kept fondling myself through the wide side vents of the overalls with both hands. I often masturbated like this after work as it was exciting and there were no hidden cameras in those days.
I had my back turned to the front door of the garage when I heard the sound of high heels clicking on the concrete and in she came, in a bit of a hurry but friendly all the same. I was embarrassed but had to show her what work had been done despite my erection. She said nothing and did not appear to notice it but a few minutes later I saw her glancing downwards and sideways. Then I realized that one of the studs in the fly of my overalls had come open and she could probably see a bit of my cock through the side of the open fly. I tried to cover the front of my overalls but my erection wouldnt go down and I saw she was smiling slightly. Then she said 'It's all right. Don't be shy. It's quite natural. I won't tell anyone.'
I didn't know what to do then. I said something like 'Sorry I didn't mean to do it' but she continued looking at it with obvious interest and to my surprise asked me if she could have a look. When I hesitated, she suddenly popped open a few more studs on the front of my overalls so there was no hiding it any more. I had even started to leak precum from the tip. 'Ooh, it's lovely' she said. 'Let's get into the back seat of my car'.
By the time I was sitting next to her in the back seat I was close to bursting. We kissed and then she hoisted her skirt, revealing pantyhose and black lace panties. She quickly pulled them off and said 'Is that better?' It sure was! She began rubbing herself down there, transferring the wetness to her other hand with which she stroked me. It felt so good I let her take over, holding her in both arms and kissing her. I felt her rub the head of my cock with her thumb and suddenly had one of the most powerful orgasms in my life, squirting all over her warm thighs and belly. She was squeezing my cock gently as I came. I think she was a bit disappointed I didn't come inside her but was very encouraging anyway. When I had recovered, she kept rubbing herself and showed me where to touch her. I had never rubbed a woman like this before and felt her dripping wet slippery vagina squeeze my fingers. Finally she brought herself off expertly and we hugged for what seemed a long time. 'That was wonderful, darling' she said.
Finally we had to clean up. She remembered her clean panties in the glovebox and put them on. I confessed I had found them and she said 'I'm glad you like them'. Now I could actually see her in them and still masturbate when I remember that. My boss never found out.
You will be glad to hear that we kept in contact afterwards.