My 2007 GMC Yukon Denali has 135K miles on it. While changing the spark plugs I noticed that the front shock appeared to be oozing oil (I removed the front wheels and wheel well covers to get at the spark plugs). Does this mean I should be thinking about new shocks? The truck appears to be riding fine.
Have you done a ‘bounce test’? I wouldn’t be surprise if it needed them after 135k miles, but it depends.
If the shock is leaking fluid then replace the shocks. If not all four then at least do a pair.
It’s one thing to lose the gas charge from a shock.
But when you start losing the hydraulic fluid from a shock, the shock is replaced.
Tester
It means you should be doing more than just thinking about getting new shocks. It should be your next weekend project.
Yup, you’re due for a new pair of shocks. When you feel how much difference it makes (and you will) you may even decide to replace the rear shocks too. You’re due.
It’s a big heavy vehicle, those shocks have been working hard for a lot of miles.
I’d replace all 4. I did that on a Suburban, Bilstein had a sale on, much better ride and control. Check out what’s available at Rockauto.
I'd replace all 4. I did that on a Suburban, Bilstein had a sale on, much better ride and control. Check out what's available at Rockauto.
Bilstein makes real good shocks for trucks. Maybe cars too…but I’ve had a couple pairs now of Bilstein’s…been very happy with them. I replaced the OEM shocks on my 4runner some 200k miles ago…and the Bilsteins are still good.
Our Ford dealer suggests replacing shocks based on age rather than any specific test. 60,000 miles is suggested. If yours haven’t been replaced yet they probably should be. This is another reason to keep good maintenance records for your car
Well I just learned that my Denali has Electronic Ride Control (Z55). As a result what started out to be a $400-$500 job turned into a $1900 job. It could have been converted to a passive but it costs almost as much 
Hopefully you replaced all 4 for $1900. RockAuto has OEM replacement shocks for a bit over $1000 total for all 4 and installation is one connector per corner more difficult than a normal shock install.
Yes, it was all four.