On your manual trans fluid there has been a lot posted about that over the years.
The most important thing is to use a fluid that has friction modifier. A common answer has been to use Mobil 1 ATF with 2 oz (1/2 bottle) of Ford friction modifier added. This is the so called "cocktail" found in the FAQ section. Another answer is use any dino ATF that meets Mercon specs and adding 2 oz of friction modifier. The friction modifier makes a huge difference in overall shift quality.
Alternatives have included the newer Ford full synthetic MTX fluid (which Ford recommends for topping off or replacement of the Mercon fluid in MTX Contiques) but also with 2oz of friction modifier added. This is what I have in my car presently. It is probably the most expensive option. Another alternative is Chrysler spec ATF+3 with no additional friction modifier because it already has a higher level of friction modifier. I have also used this and it works great. Others have posted that they have used Red Line synthetic manual trans fluid, both with and without added friction modifier. Red line has two products, one seems closer in viscosity to ATF like the original Mercon fluid and the other a little thicker in viscosity like the Ford synthetic. If you want to try and find still another alternative, the Ford synthetic MTX fluid is a 75/90 GF-4 fluid. GF-5 fluid cannot be used because it has additives that will attack yellow metals (brass synchro parts).
Do a search and you will find more than you may want to know on the topic.
On your 98, you will need a total of 2.7 quarts. Those with the newer trans (part way into the 2000 model year) only need 2.2 quarts.
