I have a KGS300.
I've had great trouble with the guard returning -- or rather not wanting to return (jamming open) -- and I think it's bloomin' dangerous.
When you do the replacement, I strongly suggest you leave the spring off the big hook-plate (the one that retains the whole sliding carriage near the saw's pivot before you grip the trigger). Gravity is quite sufficient for it to work without the spring.
The lever that pulls the wire you need rolls over a bump on that hook, and it catches there (I've replaced the hook with a new spare - no joy). It's something to do with the geometry and the fact that the return spring itself has quite a lot of friction where it wraps round.
I also shortened the return spring by about 1cm, to increase its tension - that also helped.
Removing the spring on the big hook has finally reduced the friction enough for it not to happen any more (so far), to my great relief.
I use it at just the wrong height, so if the guard sticks it's out of my eye-line (at least, hard to see). On a couple of occasions I've almost brushed the spinning blade with the back of my hand - very frightening when you realise what you just nearly did!
I think my spares came from
http://www.powertoolspares.com/, rather than Miles. A lot of the stuff for the later models will fit, and it's almost identical to a discontinued Axminster model, too.
Take care - It's a pretty accurate saw, but it is an _old_ design.
E.