C max Auto transmission problem

[Andrew78]

Hi everyone 

Recently purchased a 2013 c max Automatic and having some transmission issues. Slipping and very lumpy gear changes as well as sometimes just not finding a gear at all. Just had a closer inspection under the bonnet and there is what looks like a missing bung on the top of the transmission, I believe it should be an Allen bolt from what ice learnt by researching my fault, I'm by no means a mechanic.

And advise would be appreciated