Strut brace would defo be advisable, just a simple bar of metal with a hole in each end would do the job.
The reason why only one side is affected is because of the hideously bad build quality on the cosworths, with them not exactly being "square", and even on each side of the car, the tolerances were quoted in mm's but a mistake led to this being seen as metres!!.
A good bash will soon sort it.
tabetha