Starting problem

Sounds like the garage didn't do something correctly.

Apparently heads are a serious problem for BMW.

http://www.usautoparts.net/bmw/parts/bmw-head-gasket-world.htm

Here's a brief history and an unofficial description of BMW's position on their head problems:

http://www.unofficialbmw.com/all/engine/all_m42_profile_gasket_faq.html

Here's a step-by-step on the Timing Case ProfileGasket (aka, the head gasket) replacement for reference so you can see what should have been done:

http://www.pelicanparts.com/bmw/techarticles/101-Projects-17-Head-Gasket/101-Projects-17-Head-Gasket.htm

However, the good news is that the difficulty starting and the fuel leak may be just the result of a clumsy re-assembly in fuel delivery bar. Check out:

http://forum.ih8mud.com/80-series-tech/285535-fixed-head-gasket-but-now-have-fuel-leak.html

Now doesn't replacing a few O-rings sound better than having to tear the head off again? :-)