If 2210D is like my 1610D, its not too bad a job. But first drain some of the fluid out and see if its contaminated with water/dirt/rust (chocolate colored). If so, i recommend at least a flush with kerosene and fluid change.
You may find the axle metal sealing surface is grooved. If so, just replacing the rubber seal wont do the job. I had to cover both mine with a product called speedi-sleeve (about $40 per axle). It is thin metal and usable with the standard seal. The alternative was order new axles from Japan at over $140 each.
I had same leak problem with 1610D and found the axle fluid was real bad so I disassembled both sides, cleaned it all out and replaced all seals. The upper steering roller bearings were rusty on both sides so i replaced them also. This turns into a messy job and the upper steering arms were hard to get off (had to heat them). All parts ran about $150 (plus $80 for speedi sleeves) - the big horizontal seals around the top of the housings are expensive.
I recommend a parts manual to start with (about $50). It will probalbly be in japanese but you can use the exploded view diagrams as a disassembly/assembly aid and the numbers are readable.
If you tear into it and disassemble the lower housing guts, watch for spacers and stuff falling out when you pull the inner vertical axle and be sure and lay out in order so you can reassemble properly.
To replace only the seal (ONLY IF YOURS IS LIKE A 1610D), jack up and remove the wheel, drain that side of axle, then remove the bolts holding the plate around the outer axle. Pry off the plate and axle assembly. There will be a gear held by a large nut and washer with one locking tab bent up into a notch on the nut. Bend the locking tab flat. If you know somebody with a special tool to remove this type of nut (a big spanner?) go find them. If not, sharpen a brass drift at an angle so it will catch in the nut notches without slipping, place assembly on padded surface (old carpet) and hammer the nut around. The nut is a soft metal so thats why i recommend a brass tool to bugger it up less. Be patient, one of my axles was impossibly tight (i really had to whack it and boogered up some of the notches and the other was loose. When you get it off, remove the gear and shim spacers behind it, tap the axle out and inspect the sealing surface (should be pretty smooth - no grooves a fingernail will catch in). Pry or knock the old seal out. Clean all parts and reassemble with new seal and new gasket on the plate. If the nut is boogered, install a new one if you can get it (Danny Parker didnt have any in stock) Or use a three cornered file to flatten the groove sides back out before reinstalling. Refill with fluid.
Note when i refilled mine, it took a while for the stuff to percolate down to the knuckle - put some in, get coffee, check level, put some in, get a beer, check level ......
I ordered a parts book and all the parts except speedi-sleeves from Danny Parker. I recommend him highly. Local industrial bearing place ordered speedi sleeves for me. I could not find an online source for speedi-sleeves but recently noticed Auto Zone mentioned it on thier web site (dont know if they can get any size).
If you need speedi-sleeves, find the measuring instructions and size chart online and follow them to select the correct PN.
If your really cheap, try topping up with 85W140 before replacing the seal - maybe this will put it off a while.
