I have 275/55/19 tires on my GL450. The rear are nearly new with 95% or so tread depth. The front have about 40-50% of the new tire depth.... not near the wear marks yet

Is this ok to drive? Does the slight difference in circumference between the front and rear cause any issues for the 4-matic AWD system? Does the GL have the ability to deal with this or will it wear something out?

I know tire rotation should have been managed better, but in the end this situation is what I currently have and I'd like to know what people think about differences in circumference.
Thanks

 

I asked MBUSA tech service through their website and they advised different tread depths on front compared to rear are ok, but if more than 50% is worn out then they would advise changing both tires on that axle.
It seems that a different circumference on front or rear doesn't cause any problem. I think my tires on the rear rotate 652 times / mile and the front go 659 rotations. A 1% difference in circumference.
I'll wear the front out a little more before replacing them.