We had a lively exchange on the title subject some time ago please see: http://www.ihre-vorsorge.de/www.deutsche-rentenversicherung.de/Expertenforum-Thema.html?id=105555&dekade=1.
The experts (Frank and others) consensus was the typical refund should be be around 10% of Bruttoarbeitslohn.
Well I'm more than happy to report I have received my refund in less than two months, the only problem is the amount refunded.
On 169.5K DM in Bruttoarbeitslohn on which I paid 18.8K DM in taxes (Arbeitsnehmeranteil) that is approximately 9657 EUR they refunded, BELIEVE IT OR NOT, 454.46 EUR that is less than 5% of taxes I paid to the German Retirement System from which I will never see a single Pfennig. Ever. Something wrong here. Is there anything I can do about it?
(thanks Frank for your best wishes, didn't work this time)