power steering pump

I have a 2001 VW Golf TDI GLS with 62000 kms approx 30,000 miles on the car bought new and has been taken to dealer for all services. I had noticed a oily mess at the rear left of engine when i installed a Zero Start heater. Took the car to dealer for reg service and asked if the the mechanic could check for oil in the bottom of the engine and on the belly pan. They said there was a bit of seepage but they had washed the bottom of the engine and to bring it back to see if they could spot the leak. Well had the car there today and they checked it and say power steering pump is leaking 650.00 will cover the new one installed.When i got home ran car up on ramps and checked under car where my concern of oil leak was it was dry. Looked at pump and sure there was a bit of oil on the bottom of it but nothing to get concerned about .alternator under the ps pump has a couple of old oil marks .Are these pumps prone to leak and dealer says not serviceable need new pump Thanks for any help Gordon 1