Complex sentence: The old syntax is still quite common in jobs which have been running for over 20 years with only minor changes-these old jobs are often complex, and converting them to use the CLIST syntax would be tricky and time-consuming.
Split into simpler sentences: The old syntax is still quite common in jobs that have been running for over 20 years with only minor changes. These old jobs are often complex, and converting them to use the CLIST syntax would be tricky and time-consuming.