I've recently had my 3 piece Work Alloys refurbished at a cost of £250 per wheel.
The whole process took almost three months in total (there was a lot of chroming involved). When the wheels finally came back one of the wheels was going down to 9psi. I took it too a local tyre depot who tested it in their water tank and the leak was coming from one of the seals on the wheel, I therefore took the wheel back.
They kept the wheel for another two weeks and when I got it back it was flat again within 24 hours.
The wheel went back again (they kept it for another two weeks) and has now been back on the car for a couple of months. It does however still lose air although only slowly. I need to pump it up each weekend and it currently loses about 10psi each week.
Bearing in mind that for the price I paid I could probably have got a cheap set of 18" single piece alloys I am still not sure if refurbishing the wheels was a good idea. The car was off the road for most of the summer and the whole process was a nightmare.
Whether I get them refurbished again or buy a new set will depend on how long the refurbished alloys last before they start peeling and tarnishing again.