I have an oil leak and have been told it is a seal. on 2002 Volkswagen Beetle TDI

Had my oil changed no problem then noticed oil spots on my drive way. I have been told it is a seal. Is that a big deal to fix and is it expensive. I love my bug. it has almost 200,000 miles on it and has been the best car ever.

Asked by for the 2002 Volkswagen Beetle TDI
Need to know which seal, there are several. Is it a real main seal, a crank shaft seal etc?