Frank,
Like Steve I think you tailor the thickness to the offset in the paint striping difference. As the Delrin material gets thicker there may be some clearance issues with the slide seal, not sure. I like the Delrin approach and over several years of use I had no issues with it at all.
It appeared to me that as time went on the stripe offset started to increase a small amount again meaning there probably was some continued sag in the roller support structure but not enough to warrant going thicker. The shim shingles would have been my adjustment method at the outer end of the Delrin strip if it became an issue. It only has to "park" the slide height where you want it at the full in slide position. I used a 45 degree slope along the long edge of the Delrin (table saw cut) and then rounded the point where the 45 cut ended using a sander. The more shallow the taper the better the slide seal will conform and follow the Delrin edge. If my saw could have made a shallower cut I would have gone to 30 degrees or so. Delrin is a perfect material for this given it can be milled, won't rust, very smooth and easy on the seals as it travels against them.
To sort this out you could get a base measurement and then gently jack up the slide, measure to a reference point like the trim molding below, and see if raising it a half inch still provides the necessary clearances and the seals have reasonable contact. If not go to 3/8ths inch. Things should fit OK given you are basically going back to what the original fit was. It does not have to be perfect, just the best compromise.
Frank as far as adding bondo, I think I would just use a bed of silicone to fill the gap under the Delrin and then let it cure before putting the weight of the slide on the repair. Because the Delrin is a bit wider then the roller (you could add a bit more width if need be in the Delrin) it should go beyond the depression width wise. (Don't forget to allow for the tapered edge in the Delrin when you come up with the appropriate width of your Delrin sheet repair stock)
As far as the front slide, that is very heavy, I would probably consider a thin metal plate there if it was bad enough to require a repair. In that case I think you are preventing a wear point and not trying to build up thick material for a roller structure sag issue. Hope this helps.
Later Ed