I've been using my Topsider (that's a brand name, not a generic description) for about four years now. I've changed oil in my now sold 95 C280 many times, a friend's CLK430 twice, and my '01 C320 once. Every time it has been done with the engine at normal operating temp. Not once has the suction tube melted or gotten soft. I think this is just a theory promoted by some of the fussbudgets on another MB list.
The unit costs a lousy 40 bucks at West Marine.