From what I've heard it is a very common problem for the L36. Blackarrow continues to advise me to replace mine before I have a problem but mine didn't look too bad when I pulled it out so I'm gonna wait a little before replacing it haha.
$700 is ridiculous though, you could have paid like $100 for parts and done it yourself in an hour or two.
Also all new plastic UIM are reinforced over the original stock ones so the chances of having another problem is much, much less. Definitely would not be worth it to upgrade to the L26 unless you're going for better looks or turbo.
_________________________
1998 Pontiac Grand Prix GT
WizAired CAI, Impala 12" Brake Upgrade, ZZP Alternator Rewire and Voltage Booster, Rotated Dogbone Mounts, Kicker KS690 6x9s, JBL GTO427 4s, JBL P652S 6.5s
2001 Ford F150 XLT SuperCab
Stock, LineX, 212K