Is there any pattern to the use of the two types of exhaust grills? It seems the welded (straight, horizontal grill) are more prominent. What variants tend to use the cast version?

The exhaust with the hump at the top are from the 1st through the 3rd production batches of the first cast turret. Leopard 1A2 is 5th batch. This was not changed as the tank was upgraded to 1A1A1, etc.