Dave,

Before you send these out, make sure the breather that is on top of the drive unit, below the drive motor is not clogged. We managed a warehouse that had 40 of the order pickers and that was a common problem. Cleaned breather and seal stopped leaking. The earlier you catch it the better. Good Luck.

Can you send me the info on the parts and the shop you send your drive unit to please.
Thanks

yep, if your sending them to a machine shop then sure, he would know this, especially if he knows lift trucks.
Unfortunately this is the factory way of selling parts these days, they don't want tech's repairing parts anymore, today we are just basically parts/component replacers with laptops and some training. The days of digging into a problem and actually fixing it and learning about how and why it failed are over, that's the way they want it.
It's all about profits and numbers etc anymore.

The machine shop I send these units to do the work for me, I supply the parts needed and they press them. The man who is owns the machine shop should know this as he has been in the lift truck industry for over 30 years, or at least I hope he does?! I appreciate your help.

your only option is to get a press if you want to be replacing these seals yourself.
by design you cannot just pull the wheel off and pop out the seal because of the axle flange, so therefore your stuck having to buy these units if you do not have the means to remove the axle to get at the seal.
Also if i remember correctly if you do take the axle out there are shims and also the axle nut has to be torqued and they make a special tool to hold the assy just so you can get that torque you need on it. If you don't get it torqued correctly it will come apart.
This is one of the main reasons they made it this way (unserviceable).
Too many failures in the past from field service work because the reassembly was not done correctly.
If you know what you're doing though it can be done.