Diplomat 8332... can I fix it?

Hi.
Our diplomat 8332 has not been washing properly. The lower spinning wash arm was badly cracked, so I replaced this (£30 inc p&p!), thinking this was the cause of the problem. It is still not working though, without any faults etc. The dishwsher fills, heats and drains fine, and I have checked to see if pipes leading to other two spinners are blocked.. they seem to let water through ok, but don't spin during the wash cycle. The machine does go through the whole cycle though. I have read other posts, removed base etc... no water at all so no problem there. I think it might be a pump, but don't want (can't!) spend any more on parts etc until end of month! Does this sound fixable? If so, is it a DIY or professional job (expensive?) Any advice welcome... Happy New Year! Ben