Quoted from Otaku:The bakelite wiper is standard to all Gottlieb wedgehead games except for 1973's Pro Football which usually a special unit with a special wiper. (Actually that probably means ball-launcher games like Big Hit and others also probably used the same or a similar unit) Funny enough though, I actually swapped a Pro Football unit into my OWN Sky Jump and it works fine too.
This made me wonder so I did a little digging through parts catalogs to clarify. It turns out that it isn't far off.
The Ball Count unit wiper on Sky Jump is a B-9998 which was used on many games as far back as '67 King of Diamonds. There are however several other wipers used on Add A Ball and Italian export games. Before 1968 there were Ball Count units, Balls To Play units and Balls Played units which all used different wipers. Starting in 1968 though it looks like most (maybe all?) single player games that weren't Add A Ball or Italian export models used the B-9998 Ball Count unit wiper (including '73 Pro Football BTW).
/Mark