I've been running Syntec in mine since I got it in 1996 w/45k. I'm at 130k, and no news is good news. Improvements have been made to help with the rubber seals, but it still can cause some leakage. You may notice yours start to smoke some, too, when you start the car or during an extended uphill idle. Synthetics can contribute to that condition in a few cases due to valve seal leakage. Mine has since I changed over, but the SC is hard on them anyway,too, so some of that'* wear now. Just be aware of it - synth can cause some smoking but it'* nothing to be concerned about. You'll know when it'* the real thing becuase it will smoke all the time, but these are tough motors and you should see a good long life out of it regardless. A lady at my office has an '89 LaSabre with 260k miles running strong.
Being devil'* advocate: if you run the numbers on changing your oil regularly (3k miles) with and wo/synth, you can pocket right at $1000 over the course of 150,000 miles (assumes $5/qt Synth, $1.37 non). Many would debate whether it'* worth it if they are the car- trading type, or they just count on some major bottom-end failure regardless of the oil.
Personally, I treat every car like it'* my last and I like knowing pushing an oil change is not the end of the world if I'm in a time pinch. Plus, I expect this engine to hold up for 200k at least.