This $10 seal keeps popping up :'( It is not quite that easy. You need to pull the entire case to do this. At the minimum you will need a gasket kit and seal kit. Unless it has already been rebuilt it should be rebuilt when you pull it apart. Money well spent. Rebuild kit with everything you need is less than $200. If you pull it and install it the rebuild itself should be around 3 hrs of labor.
On the 62 case there are 2 things to watch out for:
There is a D shaped oil ring that fits on the tranny output shaft prior to the TC oil seal. It is A440F specific and Toyota does not sell them and AAMCO cant get them. Make sure the one you have is in good shape.
The bolts that hold the case onto the back of the tranny need to be sealed to prevent leakage.
I also own an 89' FJ62 (175K) in SanDiego. I had Transmasters by IN & Out Burger in PB do it and it was a nightmare. They are the most incompetent and unprofessional business I have ever dealt with. They claimed to have years of experience with Land Cruisers and other 4x4's, I was sold. They reused bearing races, twisted off the switches without disconnecting the plugs which ruined the wires where they are molded into the switches, removed the whole tranny & Tcase after trying to pry them apart not knowing it had internal fasteners, and finally putting the rear output shaft bearing retainer that holds the speedo cable 90deg out pointing up which then blocked the oil journal for the rear output shaft bearing causing it to fail less then 6-months later. They denied, avoided, lied etc. and I ended up with the short end of the stick.
I rebuilt it myself after that and it was quite easy. The biggest challenges are weight and clearance under the vehicle. If you have a clean garage, some high stationary jacks and Toyota's FJ62 Repair manual (highly recommended) it is simple.
If not, the best place I know in San Diego is Keary Mesa Toyota, they have an outstanding reputation and I have received exceptional service from them.