Thanks Harvieux, I think your approach is logical.
Regarding your question, I have maintained the vehicle since it was new but have never checked the final drive level until I found it leaking out of the vent cap. The transmission was replaced at 3,500 miles by the dealer after it developed a problem where it would drop out of gear at idle and then clank back in after the RPM went of 1,000. Everything was so clean at that time I don't know if the final drive was replaced with the tranny or not. I must say that the dealer did a flawless swap as far as everything being put back the way it was...but maybe not. In any case, I agree the next step is to check the trans. fluid level. The vehicle is now at 60k miles. I looked the final drive today and the vent cap has not leaked anymore fluid during the last 200 miles of driving. So this may be an intermittent condition.
For the record, I think the trans. oil checking procedure is the worst feature of this power plant and the problem I'm having is a perfect example of why a simple quick check method is vital for normal "field" trouble shooting. My choice is to either go to the dealer and spend at least $100.00 and hope they do it correctly or spend over $200.00 for a software tool (not to mention a lap top PC since I don't have one). In my opinion, its not a diesel engine problem as much as it is a VW engineering/cost tradeoff thing. At least the Vag-Com will provide a lot more value in the long run.
And another general comment on the economy of this car, I got my wife to agree to drive this car on the grounds of economy but when you factor in the cost of "VW’s" maintenance I'm not sure that's true. Think about it… at the 60,000 mile point, if the average cost of fuel was $2.50 per gallon (on average) there is only about a $1,700 savings over a gas car getting 30 miles per gallon over this TDI assuming it has averaged 45 miles per gallon. Now balance that against the cost factors of the pending timing belt change, this potential repair/troubleshooting cost and the amount of time it takes to keep up with all of the other little problems that need attention on this model. Sometimes this is a "hard to love" car.