I have an Oskar.... lol... we chose the "k" for it to be a bit different but also DH's father is German heritage.

Funnily enough, Oskar's middle name is LEVI...haha.... DH didn't like it for a first, but I wanted it cos my grandfather's name was LEVISON... (COOL NAME!!!) and we cut it down to Levi. The more I thought about it later though I kinda wish we'd chosen Levison, it's awesome!

I'd go with Diesel spelling if it were me.

One thing I HIGHLY recommend doing is repeating the name over and over with the surname - if it's a boy they have it forever.. most girls change it when getting married... but not always. Sometimes a first name you just luuuuurve sounds not so good put together