My '90 didn't come with one of these?

That explains why it wasn't there.

I was hoping to get out of this without opening the trans. Looks like I'm digging in.

 

I agree with a new main drive gear. If you put the updated (- '94) pulley on it, it'll be tight on the inner 1/8-3/16 of the gear splines and loose on the rest. It'll work loose and/or strip out no matter what you do.

So... you need to pull the gear set and main drive gear. Don't even think about it without the correct puller/installer tools for the main gear and bearing. It's really not that bad of a job since you're half way there already.

If you use an Andrews main drive, it'll come with new bearings installed. OEM you have to buy separately and install them. If you go Andrews, most recommend replacing the 5th gear with Andrews also on the counter shaft for quieter operation.

OEM pulley kit - 40210-85D has upgrade pulley, spacer, quad seal, nut and lock
For reference:
Main drive gear - 35029-85A
5th gear (on counter shaft) 35626-79A

 

Loctite makes a product to fill the gaps in a splined installation. Don't remember the number, but it's thick stuff. You put it on the splines, put your pulley on, torque it, etc. and let it sit and it all works out. Might consider that with a new pulley before opening the trans up for a new shaft. The Loctite product is used on Europa axles. I could look for the number if you're interested.

 

I had the same thing happen on my 96 Ultra Classic, and I replaced the 5th gear/spline, and thought it was pretty easy. I personally would not use the old spline or pully.

 

Just to clarify - the updated pulley (and most aftermarket you buy unless you look really hard) will be the later splines. The splined center of the -94 hub is longer (deeper) than original (.200) and the spacer shorter by the same amount. Thanks to Dan89 for the measurements. You have to use the later main bearing seal also because of the larger OD on the newer spacer.

 

Omaha, you`ve already done the hardest part of removing the gearset, the right side is the easy part.

When you remove the drive gear from the big ball bearing, use a puller, don`t try tapping it out.

You can make up a puller with some threaded rod, sockets, washers and nuts.

After you get the main drive gear out of the ball bearing you will also need to replace the bearing.

 

I did the threaded rod thing. Not difficult making up the puller/installer. Just use some rubber hose or tape on the threads of the threaded rod when installing the new drive gear pulley to protect the inner needle bearings/seal.

I ended up using the Andrews main drive gear with out replacing the accompanying counter shaft gear and had no noise issues. As Dan mentioned, comes loaded with the small inner bearings and seal already installed. You do have to pay attention to what years with the Andrews drive gear because I think the 95 and later requires that you must get a new and matching counter shaft gear to match the "close contact" cut of the gears.

Also used the Andrews front pulley. The bearing that Dan mentions is a 6309 C3 bearing. Get a good quality bearing. Stay away from the China stuff. You will need a monster pair of snap ring pliers to remove the snap ring that retains that 6309 bearing.

Watch a few youtube videos and you will see it's not that much trouble, just time consuming. YD

 

So I'm guessing what happened to get a leak that big that fast is the belt sprocket nut loosened up letting the sprocket and spacer slide out letting the oil go by the quad seal, if out don't want to rig anything up Ohama this tool works good for removing and installing 5th gear, https://www.ebay.com/itm/264334542636 and be careful doing so, the lip that's built into the transmission housing for the 5th gear bearing is thin and can break then your transmission housing will be junk

 

But you don't need to pull the gear set and 5th gear to fix your leak unless your going to upgrade the main shaft like t150vej was saying, if not get a new sprocket, nut, nut retainer, quad seal, wedding band seal, main seal, Loctite the crap out of it and put her back together, unless you fear your 5th gear bearing maybe going bad

 

The splines on the main drive gear are damaged, the gear must be replaced, no way around pulling the gearset.