Need a radiator pressure test.
If you’re a DIY type you can buy a test kit. Auto parts stores sell them. Or any good independent repair shop will do the test for you. What specific problem are you having?
Car overheated. Got home before engine light came on.
Oil service keeps telling me I have a slow leak, but he can’t tell where it’s coming from.
He said to get a pressure test. I won’t have him do it, because I don’t trust him.
I have 88,600 miles on this 15 year old car. Lots of short trips.
I met a fellow with the same car / year / model. He had 230,000 miles on it. “All I’ve had to do is replace the radiator, twice.”
What part of Sacramento are you in? I’m in Arden.
Dee
Sorry, I’m in St. Louis, a long way from you. In fact, I’ve never been west of Kansas. 
Assuming you haven’t driven the car since it overheated and it’s good and cool, remove the radiator cap and fill it with 50/50 antifreeze and water, plain water in a pinch. Drive (carefully) to the nearest trustworthy shop, keeping an eye on the temperature, and tell the mechanic there your car is overheating and that a pressure test was recommended. Pull over and shut it off if it starts overheating again. That will allow the mechanic to determine where the leak is and proceed accordingly.
Dee , this is a Forum on the world wide web . It is not just your area . Use the online rating sites , friends , relatives and coworkers to locate a shop that can do a pressure test .
Sorry, but not everyone gets the same service out of the same type vehicle . Just too many mechanical parts that can fail or not fail.
A pressure test, while a good idea to find a leak, may not even solve the problem. There might not be a leak. You have one guy, who apparently works for an oil change place, who you don’t trust, telling you to have a pressure test done. Tell another mechanic your engine is overheating. If he’s competent he’ll know what to check. For example, your engine fan might not be working. Your thermostat might be stuck. Your radiator might be full of bugs. You might just have low coolant because it wasn’t full in the first place. At this point nobody knows. Good luck and let us know what the problem turns out to be.
Just a tidbit: a common place for a coolant leak on that vehicle is the plastic reservoir attached to the firewall where you are supposed to add the coolant.
I am not 100% certain on this as I have my own cooling system testers but I think(?) that some auto parts houses such as AutoZone, O’Reillys, etc have a cooling system tester as part of their Loaner Tool program. Put a deposit in and get it back in full when you return the tester.
That’s for a DIYer but I would think a test even at a garage would not run that much if you had it done.
Maybe it’s nothing more serious than a weak pressure cap. It’s 15 years old assuming that it has never been changed before and that’s a lot of heating and cooling cycles to go through.