Car was MOT'd and serviced 8 weeks ago. Over the last week or 2 I suspected there was oil leaking from the car. Only small amounts, no warning lights appeared on the dash. Recently done a 200 mile journey where there was a strange smell and the car was doing half the MPG it usually does. I pumped up the front tyre today and noticed oil on the road near the front tyre. Opened the bonnet and there is no cap over where the oil goes in. Tried to open the dip stick to check to oil level. It won't open. I think the mechanic has forgot to put the oil cap back on after the service. Car gas done 1200 miles since the MOT. Planning on phoning the garage who don't the MOT and service it the morning and taking the car to them. Will this have caused a lot of damage? Any advice?