2001 E320 4M 'tie rod'?
 

Ok. the local oil change place rotated my tires and the kid mentioned a very loose 'tie rod' - it's in quotes because I didn't look at it.
I believe something is loose...as they don't fix stuff like that, it was just nice of him to notice and say something!

So...what's the best way to check this out?

Thanks!

(wow...didn't realize this was my first post... :) )

Jack up car safely and take a look. Most likely the boot is cracked, leaking grease and allowing water to enter, to corrode the fitting.

Could also be a prob with the rack and pinion. It will tell all when you get it off the ground and give it a look. If the rubber boot isn't busted give the wheel a few shakes you should be able to see where the slack is coming from.

Be sure to know the difference between a tie rod grease fitting and CV axle boot. It's bad if either is torn...but the CV would need immediate attention. The CV boots are the accordion rubber pieces on the inside of the wheel. Googling CV boot might help you know what to look for. They can best be seen by turning the wheel and looking at one side, turning the wheel and looking at the other side.

This is almost definitely not what the kid was talking about but always good to check while you're there.