I love my Mityvac. Yes it does let you add more vacuum to test a line.
I HIGHLY recommend you get one. Have it under your pillow and ready at a moments notice.
I had a leak in my front right passenger door. I haven't taken the time to fix it yet so I isolate the lock line. That fixed my leak and now my engine turns off.
Once I gather the courage to open the passenger door for some discovery I will fix it.
Until then at least the door locks when I turn the key
