380 timing chain

I might be buying a 1980 380SL (107) with 90,000 miles.
I've heard about weak single timing chains and was wondering how big an issue these are;
Do they just snap with no warning or do they tend to rattle first?
What mileage should I consider changing it?
Is it worth while upgrading to a duplex and what costs are involved?

[cbdo]

Plagiarizing a link from a similar thread above, here's a discussion of the issue:

http://www.import-car.com/ic/ic40024.htm

AFAIK, it's not that the single-row chain breaks, but that it stretches a bit sooner than the double-row. It's chain stretch that allows the chain to slap against the plastic guide rail, which when it's old and brittle breaks, which leaves a piece to get caught in the chain and cause it to jump a sprocket, which causes mistiming and valve damage in the engine that Jack built.

[suginami]

Actually,

Only the U.S. got the single row timing chain on the 3.8 liter engine from 1981 to the middle of 1984 when the factory went to the double row timing chain.

All other countries in the world always got the double row timing chain.

However, it is always recommended to change the timing chain and chain guides on M116 and M117 engines every 100,000 miles, or so.

Read this very current thread to find out what happens when you don't change the above. This forum has probably over a hundred such experiences with all M116 and M117 engines (3.8 liter, 4.2 liter, 4.5 liter, and 5.6 liter).

380se timing chain ?

[MikeTangas]

Single row timing chains on the affected 3.8L engines have/had a 30K replacement schedule, or so I seem to recall reading.

[neileg]

As suginami implies, the UK spec 380 never had a single row chain. It also had 218BHP against the 155 (I think) of the US model, so comments about the 380 being underpowered don't apply in the UK, either.

I had one of these and it was a fine car and a trouble free engine.