Other than neatness no diff between radial and axial electro's. The best way to test electro's is with an ESR meter, Ive been using this one "
http://members.ozemail.com.au/~bobpar/esrmeter.htm" for many years repairing assorted comms gear with excellent results.
Normally (but not always) the smaller physical size caps are the first to go, Ive hardly even seen ceramics fail but another type of cap (tantalum) can be very troublesome, Im not sure how prevelant they are in pinballs (my SF2 has them on most boards) but when I was repairing consumer electronics for a living tantalums were probably the most unreliable component of all, mostly they internally short and hold power rails down, blow fuses etc. They look like small expoxy dipped blobs and come in various colours.
