TL;DR

A weeping cylinder rod seal must be replaced. Inspect the rod for scoring before fitting a new seal. A scored rod will cut the new seal immediately.

What you might see

oil weeping or dripping from cylinder rod
mast drifts down slowly when loaded and parked
hydraulic oil level dropping
oil film on cylinder rod visible

Likely causes

Tap to mark as ruled out

Rod wiper and piston seals worn or hardened from age, heat cycling, or contaminated oil
Rod surface scored or pitted from debris contact, cutting the seal lips
Hydraulic oil contaminated with water or grit accelerating seal degradation
Cylinder misalignment putting a side load on the rod and causing uneven seal wear

Required tools

Toyota 8FGU cylinder seal kit
Seal driver or smooth installation sleeve
Torque wrench
LOTO kit
Clean rags and oil catch pan

Safety first

Never work under a raised mast without a mast safety lock or fully lowered mast. Cylinder failure during disassembly can cause sudden mast descent.
Lock out the forklift and depressurize before opening any hydraulic connection.

Procedure

7 steps · ~90 min

1
Lower the mast fully and lock out the forklift.
2
Depressurize the hydraulic system by operating the lift control several times with the truck off.
3
Remove the cylinder from the mast channel following the Toyota disassembly procedure. Note the position and orientation of all shims and spacers.[1]
4
Inspect the rod surface for scoring, corrosion, or pitting. Run your fingernail along the rod. Any detectable scratch will cut the replacement seal. A scored rod must be polished or the cylinder replaced.[1]
5
Install the new seal kit using the correct tools. Lip seals must be installed without folding or nicking the lip. Use a seal driver or smooth-edged sleeve.
6
Re-install the cylinder with the original shims and spacers. Misalignment will cause the new seal to fail prematurely.
7
Fill the hydraulic system to the correct level, cycle the lift 10 times to purge air, and check for leaks at the rod seal.

Sources

Toyota 8-Series Forklift Operator and Maintenance Manual, Toyota Material Handling
Toyota 8FGU Series Forklift Service Manual, mast cylinder removal and seal replacement procedures (general)
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