I posted this in another forum but no response. Was hoping someone could let me know.

Just had a conversation with my local Mercedes dealership about a car I'm purchasing purchased this Friday. Buying from someone but discussing 3rd party extended warrantees with local dealership. She was going over the Carfax with me and when she said in May 2023 at 12,000 miles the prior owner had the 40k mile service performed. This May I'm coming up on year 5 and the 50K mile service will be do soon. The car has 13,120 miles on it and she's telling me I need to do the 50K mile service, plug changes, etc.. What's that all about? Service once a year or every 10K miles. Oil is good for 10K mile oil changed BUT if you only drive it 1K in a year it still need to be changed. 10K miles a year over 5 years = 50K miles.. I can see needing plugs and whatever then but with only 13K miles on her it doesn't make sense.. Is this just Mercedes way of making money or is there something more to it?

You haven't stated the year of your car, but many service intervals are time- mileage indexed, whichever comes first. Brake fluid is a good example -- flush and replace every 2 years or 20K miles, whichever comes first. Other services, such as sparkplugs are likely debatable, but IMO I wouldn't change them at 5 years/12K miles, but I would change them at 2 years/50K miles. But if you're purchasing an extended warranty, you likely have to abide by its requirements to receive its benefits.

I have a 2019 GTC roadster. Are Mercedes temperamental or problematic vehicles? I had a 1980 Corvette. Brake lines were never flushed and never had a problem. Never flushed any of my vehicle brake lines and never had a problem. Flushing every two years seems excessive, unless of course they are prone to failure... OR they would cost so much to replace making flushing them every couple years a bargain.. I was going to get an extended warrantee and even considering the prepaid service contract BUT if I have to follow Mercedes service intervals I think I'll pass on both.

I agree -- this 2 year / 20 K mile interval seems excessive. I did this brake service a couple months ago at 4 years and 20K. The fluid I removed was not discolored, indicative of oxydation, and did not test positive for moisture content. Yet others will argue that brake fluid is hygroscopic and readily absorbs moisture. Sure, but how? Braking systems are sealed hydraulics, able to withstand pressures up to 7000 psi. But water or humidity is going to infiltrate through stainless steel tubing by osmosis? Well, maybe if you spend weekends off roading through axle deep water.

But every driver and every vehicle is different. I change my engine oil and filter every 5K miles, and others tell me I'm wasting my money. Yet others toast a set of pads and rotors in 20K miles, while mine still have 80% of their life left.

Some previously consumable parts, and fluids, that used to be changed out, are on condition now.
For instance, the platinum spark plugs, and radiator coolant.

Not everything Mercedes recommended is in your own best interest. Case in point engine oil service.

Many reasons make the 5kMi oil change interval a better recommendation to reduce unnecessary wear. The oil in use gets degraded too rapidly leaving behind cylinder scoring causing misfires faults.

I use to do 3500 mile oil changes when using dino oil. When I switched to synthetic I upped it to 5K even though at that time I was told 7500 was acceptable. Did the wife's Sequoia yesterday and the Mobil 1 container says good for 10,000 miles. I have a F250 Diesel that "monitors" the oil and lets you know how much oil life you have left. It suppose to calculate based on how your drive it or something like that. I still do it at 5K even when the monitor says there's still 30-35% life on it. Might be wasting a bit of money doing it at 5K but her Sequoia has 260K miles on her, running strong and not burning any oil.

What about the car sitting over the winter? I live in the North East. I use to start up my 1980 Corvette once or twice a month and just let her idle for a bit to come up to temperature. I heard you can get condensation in big bore engines if you don't run them often enough or condensation in the oil pan? Not sure how this could happen but heard it so wondering.

I've never given any thought to the possibility of condensation. Perhaps possible if the car is parked where the temperature fluctuates throughout the day, and there's high humidity. I'll take a close look at what comes out of my BMW when I take it out of storage this spring, even though it's been parked in my garage at nearly a constant 50F.

Did a brake fluid flush on my G a couple months ago. Bought one the $20 moisture testers. It could tell the difference between new fluid and tap water, but seemed worthless for determining 1% - 3% water. Also bought a package of the test strips that purport to measure water content by measuring copper content in the extracted fluid. Theory is that water oxidizes the copper in brake lines. Test strips showed less than 1% water, and barely distinguishable from new fluid. It's all hocus pocus -- easier to just replace the fluid and call it a day.

Correct. However, if the tester does show above the safe level, then you know it needs to be changed.

This one works well: