Have you reset the lamp in it's base as per the instructions in the Source 4 manual?
Also did you read this document "
Source Four 14, 70, 90 Degree
Lens Tube User Manual Supplement" ?
It shows they way the Source 4 needs to be focused for the best
Gel life.
You can find it on the Source 4 support page found here:
http://www.etcconnect.com/product.do....aspx?ID=20080
If only 1 Source 4 with the same Gel is burning then I would say it has to be how the lamp base is positioned.