I have poodled about on my new 250 Rev 3 for a couple of hours and found that the rubber gaurd between the rear tyre and the monoshock has already worn a hole in it.

Is this a normal problem, and are there any suggestions for remedy?

It does happen quick especially when the bike is new... you will find that as your chain wears and you mve the rear wheel back a bit things get better. They are cheap to replace and even cheaper if you grab yourself some reinforced rubber sheet and use yours as a template before it completely rips apart

Thanks for the tip.

Same thing happened on my new bike as well.

You need to buy a half link for the chain, if not it takes about 6 months to stretch and that's a lot of rubber flaps.

Just leave it, i have ridden my new bike for 5 hours on sat and 2 on sunday and there is a hole in it. I never bother to fix this, must say the new carb makes some difference.