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A 10 mm spot on a 250 mm mirror won't affect the performance very much - it's only 0.16% of the total surface area. Your secondary will block probably 20% or so of the light.
So just ignore it for the time being.
If you want to resurface your mirror, there are a few places that do it. The standard thing is to have it re-aluminised and then silicon monoxide overcoated. Cost you maybe $100 or so.
Astro Optical in Sydney used to do it, I don't know if they still do. Have a look on th net.
You can also get it silvered for quite a bit less from a local mirror maker. Have a look in the yellowpages. Make sure you give them instructions how you want it done - front surface, no protective paint! However silvering only lasts 6 months or so before it needs to be done again, but in the few months that it's fresh, its quite a bit better than aluminium.
You can even silver it yourself using the 'silver mirror test'. Have a look in a chemistry book or on the net. From memory you use silver nitrate, caustic soda and ammonia solution. I've done it a few times and if you take care it works well. If you don't take care, it blows up in your face - the solutions slowly forms explosive silver azide solution.
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