Arduino-RS232 converter baud rate problem
It is never good to base code on delays instead of intervals.  This is especially true for faster intervals where the execution of the code its self consume a significant portion of the interval.  Also note, some protocols only occasionally resynchronize.  RS232 resynchronizes after each byte (about 8 bits of data).  So any accumulated delay errors may impact the integrity of the bits furthest from the resynchronization event.

Instead of delays use the Arduino's built in hardware to send and receive RS232 communications.  The hardware is designed to work independently of code execution and will out perform software implementations especially for the faster baud rates.