I do share your enthusiam and admiration for Herbert von Karajan, Juliani, et al; my remark of "park and bark" refers to singers! I don't think conductors, as a rule, sing. Maestro Rico Saccini has been known to take over a few bars for a singer who lost it all, words and melody, to bring the artist's memory back to the performance.
From: " Made in Italy"Copyright © Rico Saccani:
"And then Houston
“Il Trovatore” is not a sing-long, but the few notes sung by conductor Rico Saccani last night were undoubtedly the first thing on the lips of the audience following Houston Grand Opera’s opening night. Those notes were a jolt. His voice came during the Act Three tenor aria ‘La pira’ covering both orchestra and singer. It was Saccani in stentorian tones correcting the tenor (Vyacheslov Polozov), who had gotten completely lost. A lot of people woke up from their dozing to attend to the podium.
- The Houston Chronicle, January 25, 1992."