I made a serial format converter using a 555 timer as the BRG once.  It
worked fine for the life of the product (such as it was.)  I put an LED
on the framing error output of the uart (an OLD uart, you understand!),
a trimpot on the 555, and adjusted till the pot was midway between framing
errors...

If you're receiving any data at all from the other side (which presumably has
a more accurate clock), you can do similar self-calibration periodicly (as
someone else has already suggested.)

BillW

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