Ahhh, the wonderful GM leaking oil cooler lines.
I have replaced so many oil lines I could easily fill the back of my astro with all of them. Many were under waranty. One of the dealerships I was at stocked about 5 pairs of each model.
The crimp is usually the problem. In a pinch you can cut off the aluminum crimp and place two hose clamps, just slightly separated, to fix the problem. You could even run it forever that way as it would probably be less likely to leak than new lines! They don't last any longer than the originals you know. I have wondered if aftermarket lines might be better, they are now available for some applications.
In the old days we did this on A/C hoses for repairs, even on the high side lines. Conversion vans still use this method on their custom made A/C hoses, and you can get replacement A/C fittings to put on the hoses at the auto parts store. For the A/C lines you can get a double clamp that has a positioning "tang" on it so you get it in the right place. You can just use two clamps though. If it works for long term (I have literally seen this last for many years) on an almost 300psi high side A/C hose containing a substance that can leak a million times easier than engine oil, it should work fine for the cooler lines.
1. Remove the Crimp.
2. Remove the hose.
3. Measure where the barbs are on the aluminum line.
4. Replace the hose back onto the line.
5. Measure to place your hose clamps on the hose in the right place.
6. Leak test and drive.
One of mine is just starting to get a bit of oil seepage and I will probably do this to solve the problem. Of course I most likely would never do this on a customer car unless it is a necessary situation. I probably won't get to it for a while (look at the in progress list on my sig).
So... Here's a quick sketch for anyone interested.
Cut on the dotted lines in the first drawing.
Do this very carefully as you don't want to cut the hose or the tubing. You need to leave the head of the crimp that the hose butts up against. Replace the missing crimp with 2 hose clamps (worm gear, band style, etc. not spring type).
You can use a cut off wheel on a die grinder, but if you do BE VERY CAREFUL. It is easiest to remove the line from the vehicle and clamp it in a vice. A dremel with a cut off wheel or hacksaw is probably the most controllable cutting tool.
As always YMMV
Hope this helps someone.
Moderators - Feel free to move to Cooling if it would be better placed there, and go ahead and sticky if you feel it's helpful enough.