Viton hose with 1/8 in ID is equivalent to the 3.2mm hose MB uses. I am using hard walled Viton tubing of this size ordered from McMaster Carr (p/n 5119K11 $3.27 per ft.) and it fits perfectly without any clamp. I have not seen the slightest tendency for weeping, unlike factory web covered hose that I installed about 18 months ago on a 603 engine. I've always felt that the OE hose leaves something to be desired when it comes to longevity.
I even removed a Viton hose to take out an injector and reused the same hose without cutting it off, I simply pulled hard with needle nose pliers and it came off then I successfully reinstalled it on the injector and it doesn't leak! Don't try that with the OE web-covered hose!
