Wizer, its your call at the end of the day, but I would break the paint seal :lol: (or not as the case may be..) and nip the plug up with an allen key, and possibly put some PTFE tape on the threads just to make it air tight .....seems a shame to go to all that trouble for something so simple, if all else fails and it still doesnt work as it should, then return it to Axminster for a replacement, but as I said your choice,
I would personally keep the larger (existing) model in preference for a smaller unit, like I said large compressors can do the small jobs , but small compressors cant do the big jobs..
HTH