still battling on...laser tube???

Hi everyone. I'm still battling with my laser, seems I get one thing fixed another goes wrong. Anyjoe i'm not having issues with alignment / focus . Focus mainly. It seems the laser isn't giving off a single point beam. I know this could be down to focussing but I've played around with that and seem to not be getting anywhere. Is there a chance there could be an issue with the laser bulb?? The beam seems to be split by the time it gets through the last mirror. Cuts like a moon / crescent shape?
There may be something realyly daft I've missed out...
Anyhelp would be great.
Thanks
Calida

Did you replace the mirrors?

Also, try grabbing a torch(with the machine turned off!) and look at the first mirror so you can see into the tube. There is another mirror. Check there is no cracks in it. Is it giving the crecent cut after going through the focusing lens, have you gota picture of the lens? It could be a problem with the tube but it could also be the lens.

Isaac