many thanks for the pointers all around ..... with these heads-up's I'm going to give an at-home r&r of the pump a go!

cheers

ps. first I need to replace the tensioner shock in my wife's '93 190E. I can't believe that MB used a M6 'torx' round head bolt to hold the top of the shock behind the idler wheel - this big torx is truly crap! the 'star' recess is so shallow that there is nothing for the bit to bite into if the bolt is even a little seized - which of course it is.