collapsed hydraulic lifter

[jsmith]

when i leave my car for several days i have found that upon initial starting, a cylinder will not fire then catch on after a few seconds. in the meantime a lifter tapping away like crazy then gradually fading to nothing. this started this past winter on a very cold day. it did not recur again until i left it for a week and happened again when i went away this past week.

my mechanic said that the lifter is collapsing, with the oil running out and the lifter losing pressure after a few days. he says that it should be ok for now since the pressure builds up and stays up as long as i drive the car regularly. i'd like to know is first, if the diagnosis is plausible and second, what it would cost to replace the lifter? what is the prognosis of such a problem - will it deteriorate rapidly? i came across a post somewhere about the cost of a lifter being replaced but i can't seem to find it...