Ballast part number and good oil leak stop
 

Does anyone know the ballast part number for a 2006 cadillac DTS? Both my headlamps are flickering (they come on blue and the slowly 'swell' to a warmer/whiter color and sometimes just flash very brightly for a bit) and I am not sure if it is the bulb or the ballast, so I am just going to replace both on both sides. I got the bulb/igniter assembly from amazon and I would like to get the ballast from amazon as well because they usually have great pricing and excellent return/refund policies. What I have found is this: https://www.amazon.com/Ballast-FITS-..._cd_al_qh_dp_i
It doesn't appear to be OEM. Does anyone have any experience with this part? Is it half the price of the OEM, so it is enticing.
I also came across this: https://www.amazon.com/TechSmart-HID...eywords=R66064
and this:
https://www.amazon.com/2006-2008-CAD...words=10391611
for much more money.

Also, I have an oil leak and I would like to try some leak stop of some kind to stave off having to get a new engine for a while since it is a 10 year old beast that I would like to sell next year that also has tranny issues with 175000 miles. I know none of these products is ideal, but neither is a $5000 engine replacement on an 11 year old car :) Can anyone recommend a 'best' brand for a Stop-Leak type of product?

Thank you everyone!

B