Aluminum is way better, and the only problems before were mainly o-ring problems, the old Dorman Elbows had o-rings that were known to leak, I went with an old Dorman nylon when I did my UIM/LIM, but I replaced the o-rings with the fel-pro o-rings that came in the Fel-Pro LIM Kit, and have had no leaks since, if I ever change it I will go with aluminum.
A while back I first put on the plastic Dorman elbows and they seeped a little. I then put on the new Dorman aluminum elbows and no problems. I almost replaced the o-rings with oem ones but decided to try the Dorman'*. I am guessing that they improved the o-rings somewhere along the line. By the way I saw last week that NAPA has them. So far so good.