There's a very short tapered entrance area, with 3 lube paths relieved into it, inside the rack that the support bushing is supposed to press into, and be retained by that tiny metal screw and its rubber seal-washer. Leaving the stock bushing in place means that the new bushing behind it has virtually no support from the housing and does almost nothing to support the rack! Further, if you fail to spot-drill a shallow dimple in the new bushing for the metal screw to seat into, an unrestrained bushing sort of floating around in there can lock up your steering in one direction- as one owner found after working on his own car. Be careful of self-described experts on steering and brakes!
For more support and possibly longer life in cars I work on for friends, I make bushings of aluminum-bronze that are twice as long as stock. But if you own a lathe, don't get carried away with this idea. If the bushing is made much longer than 2X stock size, the steering rod coupling will hit it at full lock and your turning radius in one direction will again be restricted. These racks may not have many parts but they aren't simple!
