And the filler plug on the vehicles Ive owned is also the dipstick.
I love this forum for nit picking.
Manual gearboxes have a plug you have to remove only automatic gearboxes have dipsticks.
It's not nitpicking it's just correcting wrong advice.
Ok, if you dont trust your garage to do the job, either find a decent garage, do it yourself or undo the plug then put a length of clean, lint free cloth ** into the filler hole and check that the oil is clean.
Jesus, its not beyond the wit of man to see if someone has changed the oil in your gearbox.
Or just ignore the problem and it will go away. That is the better solution that I suspect 99% of people on here will take.
** EDIT ** after inserting the lint free cloth, pull it out again to inspect it - I dont want to give bad advice.