Drip irrig. tubing - what's longest lasting in sun

Twenty five years ago I built two large drip irrigation systems at homes in coastal (cool) Southern California.
The main lines at one home are falling apart -cracking - wherever they have been exposed to sun, even indirect sun, and I now need to replace them. The tubing is a thin wall (about .040") black polyethylene, probably Drip Mist brand (or another consumer brand sold back then). Replacing the lines will be a lot of work, so I would like to use the best tubing possible.
At the other home, the main lines are intact, no cracking even if I bend them. Just surface oxidation. The tubing is black flexible pvc, by Salco. Thick wall, about .100".
Based upon the better survival of the pvc material, I assumed that I would want to use pvc to do the replacement job. But just now I googled "uv resistance" and pvc and polyethylene, and all the articles say that polyethylene has better inherent uv resistance than pvc.
I'd like to know if anyone else has long term survival info about these two plastics - or a particular brand of tubing (since some of the survival ability probably has to do with how they compound their plastic, and how carefully they monitor the quality).
Jim
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On Sat, 06 Jun 2009 12:18:17 -0700, Jim

In Las Vegas we bury the tubing a couple of inches in the soil, or cover with fabric and rock. In flower beds, mulch cover is suggested. No real worry about UV unless exposed for years on end.
I buy locally here - what the nursery suggests. Sample products:
http://www.starnursery.com/products.php?root=1
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