Roman-- I simply bought Viton O rings and used an O ring lubricant I have been using for years. No leaks from the O rings the last three months. Of course, I have other coolant leaks just to keep me on my toes.
Uhm, the tubes through the fire wall are not rigid at all! If that's the case you have an other problem..Don't bother just replacing the o-rings. You will just have the issue again.
The problem is the design and having one single screw to hold the matrix to the metal tubes that run through the firewall. Both the matrix and tubes in the firewall are rigid with no flexibility allowed. At the auction between them the single screw just does not have enough force to hold them together with all the vibrations of a car.
Best to replace it with the Audi matrix or cut the tubes after the junction with the matrix and run heater hose through the firewall. This way there is some give and flex at the junction.
Either way is better than just replacing the o-rings.
And yes I replaced only the o-rings the first time around only to do the entire Audi matrix a year later.
on left hand drive, use two sets of needle nose vise grips, gently pinch heater hoses above right side valve cover, undo heater hoses. with compressed air blow into heater core to remove coolant. inside, remove glove box, center console side covers, radio and hevac control. using a 18 to 24 inch long phillips screw driver, guide with one hand and drive with other, undo screw, separate pipes replace O rings.I did it, normal O-rings, put some grease on your fingers, roll the O-rings in your fingers so the surface has a bit of grease on it, and put them in.
Cut a hole in the center console behind the covers, the job is than done in about 7 hours, in a very easy pace.. Take your time, don't hurry, don't get stressed, it's not too hard..
Hi Rob, used coolant, since it is a slippery mess after they leak anyway. worked fine, no leaks for the last 2 years now.I'll be doing the o rings on the heater matrix in the next few days... quick show of hands from those who have done it (and not sprung a leak since !!) - did you just dip the o rings in coolant as per rave, or was anyone tempted to use rtv/ silicone/ something else as well?