eBay has cheap cyclones available, or try manchestervac's shop (just ask them)
I'd say it's worth it;
The DC07 is a pretty good vacuum cleaner, much better than any other bagless tat that's available these days, from experience I've owned all Dyson uprights available in the UK market, I can confidently say the DC07 fits into the top 5 best Dyson uprights produced, and I'm sure many will agree with me
Was it working nicely before this seal busted? Perhaps the filter got clogged due to the seal breaking as a result