Siegburg was for about three weeks under artillery fire before the attack over the Sieg river began on April 7, 1945, 11 00 hours. Have you read Ray Repasky's memoirs on the main site here http://www.6thcorpscombatengineers.com/RayRepasky.htm? That means the US troops could not have been far away from Siegburg when your Dad was there until the 16th. Siegburg was taken by the 97th infantry division. (http://www.lonesentry.com/gi_stories_booklets/97thinfantry/index.html), maybe they were also the first to be seen by your Dad, or perhaps the 13th tankers (http://www.13tharmoreddivision.org/)?
You should not send a cheque but if you like order the documents you want on your own, I think they might be more interesting for you than for the rest of the world including me - you may of course let us participate if you'll something really interesting 
The last message I got from you is of 24th.
Christoph