Been through a few fans on my dads 4i, SPAL were useless, magnets fell off the insides and jammed the motor, 100 miles away from home in Erith/Kent!!
We then used pacet, which worked better, but suffered same problem after about 2 1/2 years, fitted a Kenlowe, not a hint of trouble, drops the temps massively quicker, is a curved vane jobbie, much more costly but does the job.
tabetha