It shouldn't take months, but you need to allow for the following - examiners need to complete paperwork, the graduate office needs to process it and sometimes the corrections have to be agreed by a Dean (to make sure they are clear and reasonable). It normally does take a fortnight or so where I am. If though as is probable in August, one link in the chain is on holiday, then delays happen. It all has to be done formally but your internal might be willing to unofficially pass the corrections list onto your supervisor to speed things up - just depends if they're a stickler for doing things by the book or not. So I really wouldn't worry at this stage but if you haven't got it in another fortnight, then I'd start pushing a bit.