IMO...having been in the repair business for 30 years ,a lot of those in the 4WD world and installing a LOT of bearings.....the nylon separators between the rollers in not a problem.The load is carried by the rollers themselves.All the failures I have seen are heat related due to no lube ,water or adjusted too tight.It is true tho, that the only place I have seen the nylon used is on light duty applications .With the quality of lube available today, you should not have a problem using nylon or steel.