Paul, there are very few bad enlargers in MF, so anything made in the past 30 years that has been looked after will be good
As Ian Grant points out, Durst were the most common manufacturer in the UK and still have a good service and support vendor - http://www.northernphoto.co.uk/
The Meopta Magnifax 4 was also both well regarded and good value for money.
Enlargers are simple devices, so there is little to go wrong unless they have been misused or dropped
As well as EBAY, NOVA (http://www.novadarkroom.com/cat/203/Enlargers.html) and Second Hand Darkrooms (http://www.secondhanddarkroom.co.uk/...k/info.php?p=3) are always worth a look.
If you get a Colour Head its very important to make sure it comes with a working stabilised transformer
It’s also worth investing in a good Enlarging Lens