Personally I would say you are probably better off getting a pair of new track control arms. That way you will be renewing all the rubbers, bushes etc. Fit and hopefully forget for another 10+ years. Also likely to improve the handling and stability of the front end of the car. I would not replace just one side as this could lead to an imbalance of compliance and line straight line stability.
An alternative option is to rubber glue the split but this assumes that the general health of the rest of the rubber is OK, not hard, cracked or perished.