Engine starts difficult when warmed

What is your question?

Engine cold start in morning no problem but after its been running and sits for 15 minutes or more, it's takes many cranks before it barely starts. I replaced the coolant temp sensor with no result. Someone told me it could have a leak in one of the injectors. Other than that the car runs strong it has only 160k.

How long has your 1997 BMW 540i had this problem?

A year more or less