Upper Arm Bushings
The upper control arm bushings cannot be predicted as "bad" or still "good", based on mileage alone, especially if they have been already replaced by aftermarket parts. The reason for this is that the properly installed bushing, factory installed, allows no movement between the ends of the bushing clamped between the support bracklets, and between the rubber-to-metal "bond" between the OD of the rubber itself and the ID of the steel shell surrounding it. That is, ALL the movement occurs as FLEXURE within the rubber. Flexed rubber does not "wear out", but the rubber compound changes chemically with age and temperature, and in time becomes harder, or softer, this allowing either cracking of the rubber, or slippage between the rubber and brackets or the steel shell.
Careful visual inspection of the part of the bushings exposed in the installation, can reveal a lot about their condition. Cracking of the rubber, or "mushing out" of it at the ends of the bushings, pieces of rubber missing, or a shiny appearance at the bushing ends where clamped between the brackets, are a good indication of replacement need. The BEST test is to separate the ball joint from the steering knuckle, and move the control arm up and down by hand; it should resist moving, offering resistance to being moved; free and easy movement is a sign of bushing failure.
Bushing shells are pressed into the control arm, not a ready process for the do it yourselfer. The entire arm, with new ball joint and bushings already installed may be replaced more easily. However, this MAY affect caster angle enough to cause unacceptable steering response. Further, dimensional differences of the mounting points of a replacement arm MAY affect camber angle which affects tire WEAR; either might require re-alignment. There you have the worst case possibilities, but you should be aware of them.
FWIW, the UPPER ball joints carry much less load than the LOWER; therefore, the lower are much more susceptible to failure. Still, uppers DO go bad. If the upper ball joint rubber seals ARE cracked, as you were told, it IS time to replace the B. J.s. Look at them for yourself! imp