It's probably not worth trying to fix the old one.  Usually it's a seal gone out, but there is likely corrosion around the seal area that will make the new one likely to fail before too long.  Personally, we have gotten the best buys on washing machines by buying whatever is listed on Craigslist for 50 to 100 dollars.  In our case there are lots of them listed because of all the military families moving into and out of the area, but a washing machine doesn't seem to have much resale value, and if you get three or four years out of a cheap one you are money ahead.  Our last set is about eight years now and still working.