TopiToo,
The holes around the side are indeed to remove the breather from the engine.
What you need is a "hook spanner". I got mine from Farnell. Here's a link to the tool you need:
http://uk.farnell.com/jsp/catalog/vi...?prodId=225254.
Only problem is you need a minimum order of £10 before VAT. I just got some TV remote control sized batteries to bump it up over the £10 mark.
Hope this helps,
Neil