Peugeot 307 XS leaking oil

Hello friends, I went to a routine oil change on November 24, and I came to Van Cute Service to change the oil. About 200 Km distance to my home. When he was just about to get home, the oil indicator showed a line missing. The other day I checked it from the dipstick, I did not see any significant decrease and returned to normal on the indicator. But at times the indicator (000-) showed a line missing. Today, I parked the car on a clean flat ground in the evening, when I got up in the morning, there was an oil drop with a radius of 1.5 cm and a small drop next to it. I am a novice yet, I do not know where to look and what to check. But there is no huge drop, I just know it from the dipstick. Do you think the problem might be coming from? What would you suggest me to do?

look at the dipstick when the engine is cold, first remove the dipstick, wipe it with a napkin, then put it back in and then take it out again. If the oil plug in the crankcase is not tightened well, oil may be dripping from there, leaning under the vehicle, I think, look at that part

I looked at the dipstick, it looks 7-8 mm close to the second line above. When I look at gold, I write to you what I saw again.

Look at the oil cubes before starting your car, there is a lower line limit and a upper line limit, I think 3.25 lt. It is put on 307 vehicles and every time you change the oil, change the seal of the plastic cover of the oil filter and make sure your master replaces it.

Frankly, because I changed the oil in the service, I trust that it will be smooth, but that means there will be problems until I find out that it is not the definitive solution in the service. I think the service must have changed the gasket you mentioned.