Q.

We have a 2005 Toyota Sienna with 52,500 miles on it (I don't get out much, I know). I drive like an old lady, and it's been a pretty low-maintenance vehicle until recently. During its last checkup, we were told that it needs a new front differential seal, new rack-and-pinion assembly, new timing belt/water pump, new transmission pan gasket and new rear shocks, all to the tune of $4,800. We still have two kids living at home, and a third who frequently accompanies us on vacation trips. My husband drives a Prius, and we both like it. It has always been our intention to replace the Sienna with the larger Prius V "when the time comes." Now we are trying to decide if the time has come. We talked to a local dealership about a car on the lot, one of the station-wagon-style Prius V's. They offered us $7,000 on our car as is, in trade for the Prius V. Of course, we have no payments right now on the Sienna, and pretty low insurance rates. All of that would change with a new car. Then again, we'd have a new, presumably very reliable car that gets great gas mileage. What to do, what to do? Thanks!

RAY: If ever a second opinion were called for, this would be the situation.

TOM: That's why she wrote to us, you dope!

RAY: I mean an informed second opinion.

TOM: There are two things you want to find out. No. 1 is: How much of this work is actually necessary? I'm not saying it's not needed, but with only 52,000 miles on the car, and you driving like an old lady, it would surprise me if the rack and pinion were gone.

RAY: The timing belt and water pump should be done, just based on their age. And it's possible you need the other stuff, too, but a second opinion would tell you for sure.

TOM: The second question is whether you're being overcharged for whatever work you do need. Off the top of my head, being generous, I'd say the differential seals should cost you about $400, even if you do both of them.

RAY: The timing belt and water pump - again, being generous - should be no more than $1,000. The rack and pinion, if you need it, is another $1,000 or so. The transmission pan gasket is $150. And let's say the rear shocks are $400. That's $3,000, not $4,800.

TOM: That's if you actually need all that stuff. So take it to another mechanic and ask him to go over the whole vehicle from top to bottom, and see how his diagnosis and price match up with the dealer's.

RAY: If you don't have another mechanic you trust, go to mechanicsfiles.com, and search using your ZIP code. That's a database of great mechanics who have been personally recommended by our readers and listeners over the years. No one gets to "buy" a good review on that site.

TOM: And if you really want the Prius V (which we can tell you're dying to get your hands on), you can still go ahead and get it. But you might be better off doing the necessary work on the Sienna, for maybe half the amount these guys quoted you, and then selling the van yourself for $11,000 or $12,000.

RAY: But whatever your plans are for the Sienna, we'd recommend a second opinion before either trading it in or dropping five G's on a 10-year-old car.

Q.

I have a 1985 Mercury Grand Marquis. Recently, the oil-level light came on, so I checked the level on the dipstick. It was in the safe zone. So, which do I trust, the dipstick level or the idiot light? Thanks.

TOM: In dipstick we trust.

RAY: The dipstick almost never lies. It can give you a false reading if you use it incorrectly - if you check it while the engine is running, or just after it's been shut off and there's still oil in the upper part of the engine that hasn't drained down yet. But generally speaking, the dipstick tells the truth.

TOM: You're lucky in that most cars don't even have an oil-level light. They have an oil-pressure light, which only comes on once the situation is a "pull-over-right-now-and-shut-off-the-engine" emergency.

RAY: But your car, and some other Mercurys, came with an oil-level sensor that plugged into the side of the oil pan. That gives you an early heads-up, well before it's an emergency.

TOM: It's a great thing to have. I don't know why every car doesn't have one.

RAY: But after 30 years, for some reason, your oil-level sensor decided to croak.

TOM: I definitely would replace it. It's inexpensive and easy to install. And it's great to have, especially on an older car, which is increasingly likely to spring a leak or burn some oil.

RAY: The time to replace the sensor is next time you're having your oil changed. Once the car is up on the lift, it's a five-minute job.

TOM: But in the meantime, the dipstick will give you an accurate reading. Check it first thing in the morning, when the engine is cold. In fact, you can pad out to the driveway and wipe the dipstick on your pajamas.

Got a question about cars? Write to Click and Clack in care of this newspaper, or email them by visiting the Car Talk website at www.cartalk.com.