Yea it really depends on where the failure is in the vanos. If you head on over to m3 forum . net there is a huge amount of information about the different VANOS failures and how to fix them.
The common failure areas of e46 M3 Vanos are as follows:
VANOS sealing plate
Problem: VANOS sealing plate comes with o-rings rated for 212º. Sometimes it gets hotter than 212º in there.
Solution: Beisan systems VANOS sealing plate. Come with o-rings rated for 400º.
http://www.beisansystems.com/procedu..._procedure.htm
Price: ~$40 for part (final price TBD, being release november 2011)
Labor: 1-2 hours
DIY difficulty: 5
VANOS solenoid failure
Problem: cracked solder joints in the solenoid coil pack resulting from cold solder joint, heat cycling, and mechanical movement
Solution: Beisan systems rebuilt VANOS solenoid pack-- OEM with extra strength added. (or DrVanos)
http://www.beisansystems.com/procedu..._procedure.htm
Price: $300 (after core return)
Labor: 1-2 hours
DIY difficulty: 5
VANOS bolt failure, which can lead to engine failure
Problem: intake cam sprocket bolts back out over time and eventually sheer.
Solution: Z4 M S54s use an updated bolt design that is make of harder steel. Combine with loctite.
Price: $5 for parts
Labor: 5-8 hours
DIY difficulty: 7
VANOS exhaust cam sprocket tab failure
Problem: tabs that connect the cams to the sprockets break off over time
Solution: Dr. VANOS replacement. Cryogenically frozen for extra hardness and larger tabs to take the slack out of the system (reduce stress).
Price: $800 for part
Labor: 6-9 hours
DIY difficulty: 8
Dealer's only ever quote on entire VANOS replacement which is very expensive, so rather find out exactly what part of the VANOS has failed and fix that part only as above.
