FWIW
Here the deal with slide yoke of aft & forward propeller shaft (AKA aft and forward drive shafts) and spiders.
The slid yoke seal, is a double seal, with inner lip pointed inward. What happens is, as grease is pumped in cavity, grease presses on seal tightening it. This creates a great deal of pressure within the cavity. This pressure can warp the backing plate, and then grease will ooze out it (back plate). It is suspected, that this pressure, if not released, can result in damage to transfer case and or differential(s),
1) Toyota has changed the recommendation (seen in 200 series FSM) to: "pump in grease until yoke shaft is seen to just begin to extend". They no longer recommended lubing until grease passes seals on the slid yokes.
2) With some patience and special techniques, we can pump in grease until it passes good seals. But not recommended for the inexperienced!
3) Older high mileage, that have not been regularly lubed, seal(s) may be damaged/worn/cracked. In these grease will pass seals rather easily compared to good seals. Those slide yokes tend to need lubing more often.
4) If while pumping in grease, slid yoke extends more than 1/8" and stays extended. Remove the grease zerk for a moment to relieve excess pressure.
Always pump grease in rear propeller shaft slide yoke with wheels on ground and suspension in neutral position.
Always pump grease in spiders (AKA U-joints) until clean grease is seen flowing out.