Look carefully for rust. The main places would be on the undercarriage, the inside of the wheel wells and the wheel well lips (if the car has chrome edging around this wheel wells, this is often added to hide rust); bottom of the door panels, and inside the trunk (remove all mats and look down the sides of the trunk). I have only seen perhaps 5 6.3s in my life that DID NOT have rust in some manner, and I've seen a couple hundred of them all around the world.

The suspension isn't a problem if it's been properly maintained. Unfortunately, most owners don't put the maintenance required, every 5-10 years, into keeping it operating properly. So it's probable that you should count on $4,000 for a suspension rebuild (this mainly entails a set of 4 new rubber airbags, set of 4 suspension control valves, any air-line work, and labor). If the car "settles" down in anything less than two weeks, then the air suspension needs attention. Again, unfortunately, 90% of 6.3s need attention in the suspension department. Deferred maintenance.

Transmissions are pretty reliable, though most suffer the common "leakdown" problem inherent to MB fluid-coupling units whereby the seals harden, and gravity causes the fluid to leak past the internal seals into the bottom of the fluid coupler. This causes slippage upon startup. What you have to do is let the car idle for a minute or two after starting in order to let the fluid circulate, and the seals to saturate with tranny fluid. What it REALLY means is that a rebuild ($5,000) is in order, but you can get away with not doing this for a while. Otherwise, the transmissions are pretty reliable.

6.3s often have other issues such as starter, alternator, or water pump problems. Most 6.3 mechanical parts can be rebuilt by a competent shop, or purchased as rebuilt units from Star Motors (www.300sel.com) after sending your defective unit in as a core. Often Star Motors has rebuilds on the shelf and can drop-ship the same day.

All rubber window, door and trunk seals (all rubber on the car, actually) should be considered suspect and candidates for automatic replacement. This includes all rubber hoses (fuel and coolant) under the hood. 90% likelihood that all (what I call "chassis rubber") motor mounts, front subframe mounts, transmission mount, flex discs, rubber bump stops on the A-arms, and other rubber needs replacement. Budget $5,000+ to have all of this done.

The biggest issue with 6.3s and other 108/109 cars is the fact that previous owners have deferred maintenance to such a degree, that wheelbarrow-loads of money are required to bring them to a reliable condition. Combine that with the cars' age being 35 years old, and you have the natural disintegration of "soft" things like rubber parts, horsehair seat pads, and so forth.

I won't even get into items such as leather and wood cosmetics. To re-do the interior of the car to a high standard, budget $10-15,000.

Good luck!

Cheers,
Gerry