Yes, OLT Express operated flights to SEN from Dresden and Saarbrucken for two weeks in late October/early November coinciding with the school holidays in Germany. They used F100s. SEN management wanted nothing to do with this ill-timed start and preferred a springtime commencement. There was no mention of the services on the News pages of the SEN website. Here is a photo by Wayne Alderton of one of the F100s at SEN:
OLT Express are advertising SEN to Saarbrucken and SEN - DRS starting 18th March 2013 and DRS -SEN over the Christmas period. You can see the details here:
OLT Express - Flight schedule - London (SEN)
The lack of marketing by OLT Express was breathtaking; even their website had no English language option (although this has recently been installed). Hoping to establish a route within seven weeks of announcing the idea was, er, ambitious..... The whole story has been a model of German inefficiency. With proper marketing routes to London from Germany via SEN should be successful - shorter flight distance, no worry about the London TMA, rapid transit through the terminal to the train all make for a swift and hassle-free experience.