SPL Driveline was Spicer’s improvement for making their driveshafts not only last longer but made them significantly stronger. The new design is in the slip joint section; what they’ve done is made them non-serviceable by adding in a long rubber boot that is clamped at both ends. This keeps the dust out and the grease in.
Now although they advertise it as non-serviceable we highly recommend at least once a year to add a Spicer grease pack (Part #232799) into the slip yoke. The male spline portion of the slip yoke is coated in Glidecote a plastic like material that aids in the slip process. When there is a lack of grease, the Glidecote wears off and there will be up and down play in the slip yoke causing vibration issues. It is very important that the slip joint is greased otherwise in extreme cases the shaft can seize and cause damage to the differential and power divider.
Spicer Life Series was designed to accommodate faster axle ratios without sacrificing life of the product.