how can I make it last longer what can I do
I would get a cooler about 20 gallons. Add motor to cooler and pour melted acrylic into cooler all over engine. Let acrylic cool and harden. Take acrylic encased engine out to the middle of Neveda and dig a hole 20 feet deep. Toss acrylic encased engine into hole and fill it back up with sand. It will last forever and guaranteed not to be a problem ever
Ok so on the serious side! I am not a long time MB-er but my lawn mower, weed eater, motorcycle, and cars all last forever. SO this is little different then any other motor.
With the other responses not much to add really just keep up the maintenance, dont run lean, and watch for excessive carbon build up. I am settleing into a weekly inspection on all parts (non-motor) and bi-weekly on motor. It may be overkill but I like tinkering with it.