My E320 had the same problem before. I replaced the pressure regulator and the hard starting problem is gone. You can do it youself. The pressure regulator costs only around $40.00. You need a locking ring remover/compressor to do the job.
94 E320 Silver 210000 miles
94 740il Pewter Green 97000 miles- Retired
05 S430 4Matic
07 Lexus IS250