I'm looking for a reliable and trustworthy mechanic who works on Mercedes diesels (specifically a '99 E300).  
I'm in Gilbert.  
Any recommendations?

I've had work done on my S500 at what used to be "Phoenix Motorcars" Mercedes dealership, downtown on Indian School.  Took it there for an alignment, turned out my front end was getting jacked up.  Had them replace some stuff.  Gave me a rental, no charge.  Priced fairly.  Good communication, they speak the language of auto repair.

It appears they have been acquired by MB of Scottsdale and relocated to a new location there.  They might be worth a try although they are probably quite pricey.

It's on the wrong side of town for you, but don't go to the Arrowhead MB dealership on the West side.  I took my car there to reset the computer after replacing the crankshaft position sensor.  They weren't exactly falling over themselves to be helpful, friendly, or anything else.  The service advisor I wound up with didn't speak the language and had to go back and forth between me and the techs to figure out what I wanted (I wanted the car hooked up to STAR and the SES light and adaptations reset).  She paid most of her attention to her texts and acted like my presence was an inconvenience.  Also charged me a shitload of money and didn't detail my car.  That's not how it's supposed to be done at the MB dealership.  

What exactly are you having done?

It's a couple fuel leaks. One is likely an injector or injector seal on the rearmost cylinder. The other is something under the intake manifold, maybe the fuel line from the tank or maybe one of the post-filter lines, not sure. Doesn't appear to be anything major, from what I can see, and I would normally do it myself but don't have the free time right now.  

Not a complicated procedure on either leak, but I'd rather use someone who is knowledgeable with MB's.