I replaced my factory radio with a high quality Jap one and AM reception is still very poor, even with the antenna amplifier plugged in. I think we just have to accept the fact that Sprinters do not get very good AM reception because of the antenna design and the fact that AM reception never has been very good in any vehicle. Perhaps the HiDef AM radios and stations are better?
I only listen to PBS on the FM band, personally, as the rest is mostly garbage in my opinion. I usually just listen to my iPod through the radio.
pgr