Don't use oil on the slide. It drains away and leaves your slide dry. Oil should only be used in places like hammers, triggers etc... Any rotating or pivoting part.
You want to use grease on any parts that slide against each other. Grease stays where you put it and parts that are under load and slide against each other you want the lubricant to stay put.
Exactly!
You do not need to buy "gun grease." Go to Wal-mart in the automotive lubricants section you should find lithium based grease. They will probably have a heavy duty and regular/lite duty grease... use the regular. That tube of grease should cost less than $10.00 and it will last a long time. Use Q-tips to grease the frame slide rails and the recess of the slide. Reassemble rack back and forth a few times and wipe off any grease that leaches out.
While you are in the auto section of Wal-mart pick up a quart of automatic transmission fluid (ATF). I use this as a general purpose CLP oil. It may not smell as nice as Break Free but it costs a *lot* less.