I have a front I keep trying to email. Doesn't seem to go through.
And here is the matching rear wheel on eBay
Mercedes E Class AMG Wheel 99 02 210 Type 18x9 Rear 5 Spoke 560 65240 | eBay
I'd call them and verify the ET just to make sure.
For some reason everyone forgets to specify the ET on wheels, and its just about the most important measurement needed for a good fit.
For the Buyers sake, the ET measurement moves the wheel either closer to the outer fender, or closer to the suspension, (Inside the wheel well). Each car is designed with it's own specific ET, along with the wheels made for it. Each car has a range of ET's that will fit and a sweet spot for the best fit.
ET's that are numerically low move the wheel torwards the outer fender. ET's with higher numbers move the wheels closer to the suspension. Hence an S class wheel with an ET of 44 has a hard time fitting an SL thats designed for a ET of 30, even though the wheels look the same.
Also many different models can share wheels, as the basic design of the suspension can be similar.
In this case a W210 (E55) rear wheel is used on a R129, (the first three numbers of the part number are the model car they are designed for), as the E55 & SL's like yours share similar characteristics for rear wheel ET requirements.
So it looks like you may get the wheels you need, good luck, let us know how you make out.