About to buy an 87 300SDL. I need to know if the seats are supposed to be springy. Thanks!

Springy?? Probably not in that sense. My two both have worn out front seats, where the springs are broken and while sitting, you feel like you're in a low rider.
Seats seem to be one of the weak points of German engineering.
There are a number of ways to fix, the cheapest being pool noodles, and the most expensive is the replacement spring set.
I dealt with the seat as the rest of both of my cars were in good shape.

I think a good seat would be firm...

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87 300SDL - 215K Miles !!
99 F-350CC Dually PSD - 190K
86 300SDL - 189K
All on B-100

Yeah, they're kinda bouncy and wiggle around. Is that good?

Don't know about the 126, but my 124 has fairly springy seats. Springy yet supportive ... i.e. they don't just creak and collapse beneath me. I'd think springy would be better than saggy. But if the rest of the car is nice, I wouldn't let iffy seats be the dealbreaker ... I mean even if the seats have gone bad, you can repair them using pool noodles ... some folks here have done that, and I'll bet you could get a good DIY from a search of shopforum.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

The condition of the seats is the least of your concerns with that vehicle.

Now that's funny! True also.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Yeah all W126 have seats with some spring to them.

Now lets talk about the important stuff. How is the rust, and head? Oil cooler lines?

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200