tandem pump discussion

Can the tandem pump fail only on the vacuum side? I have a loss of vacuum, a hard ticking sound and a lot of oil around the rubber vacuum brake boost connector located in the firewall near the battery. That connecter is so gooey it has swelled to the point of no seal thus hard, crappy brakes. There is no other oil anywhere near the rubber block. It must be an internal seal issue with the pump. The engine runs perfect and no fault codes. The cam lobes all look great too including the small one in the back.Yet the ticking is rather loud. I need to pinpoint that noise source and would like some advice. My next move is to remove the pump and inspect it and it's slotted driver on the end of the cam

In my experience the ticking sound goes away once you fix the vacuum leak. I had hard brakes and the disturbing ticking after a battery change once, turns out I accidentally removed the vacuum line going to the brake booster. Once reconnected everything was fine, no ticking sound. Use a gauge to see if your vacuum is healthy after sorting all leaks you find.

In that same area, the coolant flange has a nasty habit of crumbling so I'd change that for sure.

In answer to your question, yes the tandem pump can fail only on the vacuum side.