I'd like to first thank all moderator's, contributers & especially Auditech79 on this forum, for taken time out of their busy schedules to answer concerns of all members/readers with common, and specific issues regarding "our" rides. - Very much appreciated!!!

I have a 2005 A8L with about 67K miles on it, which generally runs well. About a few days ago I had a leaking radiator replaced, and an oil change done ( I having been using CASTROL 5W-30 FULL SYNTHETIC).
After I picked up the vehicle from the mechanic, who by the way is very good and competent. I noticed that, there was some loss of power, and a ticking sound. So, I took the vehicle back to the shop, and the mechanic mentioned it was a hydraulic lifter problem, which is a common problem, usually due to low oil levels or faulty lifter. In my case he said it maybe due to air bubbles, and he added some synthetic fluid called RESIN or something like that, which after driving a few miles should resolve the problem.

But the sound is still there, and I still feel there's a slight sluggishness with the immense power I used to have at a slight tap of the gas pedal. Can anyone please help me with any suggestions or ideas to restore loss power and the ticking noise - lifter problem as diagnosed. In fact, I'd like to have some ideas and information to pass on to the mechanic when I take the vehicle back to him this Wednesday August 12, 2009. Thanks in advance for your assistance and suggestions.