One more suggestion from this ole cabinetmaker n’ fixer-upper is that you don’t worry about the drawer “slides” until after you get the rails inside the cabinet repaired because doing that will probably solve all your problems.
Now I say that because most all of the “wear” on the drawer “slides” will be on the back end and very little to none on the front end, therefore, even though the “wear” on the back end will cause the back end of the drawer to “drop” down some, but due to the length of the drawer, it really shouldn’t be noticeable when looking at the front of the cabinet.
Now you can check those drawer “slides” ahead of time to see how much “fixin” they need ….. by placing the drawers on a flat tabletop so that they are resting on the “slides”, …. then placing a “square” on the table and against the drawer front …… and the “gap” between the square and the top of the drawer front not only tells you how much the back end of the “slide” has been worn down ….. but how much the top of the drawer is going to be “off vertical” or leaning back in from the top edge of the drawer opening.
Now I don’t mean to offend anyone by offering a different opinion, but if I have, I apologize. And so that you will know where I am “coming from” I will post pictures, … in a “new” post, …. of a couple cabinets that I made for the wifey. But first I’ll have to “upload” the pictures to Photobucket.
Cheers