Bolt missing after gearbox service

Hi All 

My 2015 Audi A6  s tronic 7 speed gearbox was serviced at the main dealer last week , while they were changing the oil they said the seal had a leak so had to do extra work rather than a regular gearbox oil change,  total bill came to €900 . I checked under the car today 7 days later and notice a bolt missing , i dont exactly know what this bolt is holding but I assume its supposed to be there . I will be contacting them back on Monday to tell them but in the meantime can anybody tell me what this part is and will I get away with it for a few days considering thete is another bolt at the other side holding the part in position.  

Thanks