The 380 SEC was, I believe, the first SEC built. The little 8 cylinder is peppy but no match for a 500 or 560 in acceleration. Nonetheless, a friend has one he's owned since 1985, and he's looking for a complete gray interior to replace his. This is a gas engined car with 235k miles on the engine.
There are actually two weak spots on this engine. The single row timing chain is well known and obviously needs conversion if not already done. The lesser known weak spot is the cam oiler elbows. Each cam has a metal oiler tube above it to keep the oil on the lobes. Unfortunately, the tube ends have phenolic plastic elbows on the ends to make the turn. My friend's 380 lost a cam at around 100k miles when one of the elbows cracked and oil-starved a cam. MB actually picked up the tab for his independent dealer friend to rebuild the engine as long as they got all of the parts for examination. He ended up getting a little extra engine work done to make it a little more stout, including the couble row chain since they pulled the engine, but the car runs very strong 135 k miles later.
If you have a 380 (or any of the V-8's of that vintage) check above the cams next time the valve covers are off. The elbows are simple to replace and only cost about $10 for both sides. I replaced the ones on my friend's 380 at around 210 k miles just to make sure he wouldn't get surprised again.
I personally like the 380 over the 560 but I'm not a horsepower junkie and the market favors the larger V-8's. If I were looking for a toy, I would probably look for a well cared for 380 SEC, but that's just me.
In any case, the SEC's all had the same chassis and were designed as a driver's car at a time when MB didn't care about the economics of marketing cars. They have incredible manners for a 20 year old design and still look great on the road.