From memory (and it's been a while....) they are easy to fix. Being so large there is lots of space to work, and from memory (well either the #4 or #5) has the shutter blades screwed in to the backing plate, so when oyu dismantle it things don't fall out when you least expect it....

I found these pics on the web - they should help you...

http://www.flickr.com/photos/tomshue...633924/detail/

have fun!

Andrew