Original sentence: They generally consisted of twelve car trains with a  4 REP electric multiple unit at the rear while the leading units would be unpowered 4TCs
Edited sentence: Occasionally only one TC would be taken to Weymouth with the other being left with the REP at Bournemouth.They generally consisted of twelve car trains with a  4 REP electric multiple unit at the rear while the leading units would be a pair of unpowered 4TCs