Brian -
The 76673 tub repair kit and the 21365 washers are either/or parts. The repair kit installs in the same place that the 21365 rubber washer does, however the kit is designed to cover a much larger area and to elminate rusty holes near the orignal 21365 washers. You only need one repair kit, and considering the price now for the 21365s, I'd just get a kit and use that.
As to where to get them - there are only a few aftermarket sources of parts, Gemline (now SUPCO), EXACT Fit, RobertShaw (I think now a defunct line), maybe a couple others. FSP is Whirlpool's name for their parts, like Motorcraft is for Ford, Mopar for Chrysler, etc. There are LOTS of FSP distributors out there, so if you find a seller with FSP parts that you like, take your pick. Sears is a good place to get stuff as Laundress said, mostly for their convenience but they can be expensive. They probably have a parts diagram online for your machine.
For your machine, definitely get a 383727, a 93553, and a 76673. The only other seals you could need are spin tube (bearing) and agitator shaft seals, and unless they are really gross when you get in there (I doubt they are based on the look of the goods underneath the baseplate), I'd not bother with them yet. In fact, I wouldn't touch anything underneath until you have the leak fixed, if you are already satisfied with the machine's mechanical operation. To change the bearing-spin tube seals you will need to pull the upper spin bearing, and that's a beetch of a job for a beginner.
Let me know when you have the parts!
Gordon