Here are some scans from the literature.
As mentioned by daringhart13, 1972 was a key year.
The Organization book (1972) said that if an elder committed a serious sin "some years ago," and it was found out, he should be removed.
The Kingdom Ministry, October 1972, explained that "some years ago" meant 2 or 3 years, although it was not an exact number. However, if the sin was committed 3 years ago or more, then the elder did not need to be removed.
How in the world they arrived at these numbers is anybody's guess.
"Organization For Kingdom-Preaching And Disciple-Making" (1972) p170, par2
"Kingdom Ministry", Oct 1972, Question Box p8
I'm not sure what was said on this topic between 1972 and 2010, but here it is in the latest Elder's Manual.
"Shepherd the Flock of God" p38 (2010 Elder's Manual)
Notice that "child abuse" would only "likely," not definitely disqualify him, for "many years," not permanently.