1998 lifter problems?

I recently began hearing a tapping when starting my 1998 silverado, it doesn't matter if the engine is warm or cold. it goes away after a while. i am pretty sure that it is a lifter losing prime, but not positive. i just noticed my water pump is leaking. it has about 70k miles on it. the truck has 173k miles. it has been good to me. i have never been into the engine before. i am trying to make it last one more year. the intake manifold has been leaking for a year or so, just enough to tick you off. i was thinking of replacing all of it at once. here are my questions--
should i replace all of the lifters or only those that are either sticking or losing prime?
do i have to remove the intake to replace the lifters? (if so i will fix that gasket at the same time)
if the lifter(s) are bad, is this a sign of more problems sooner than a year from now?
is there anything else you would do while you had the engine partially disassembled? what about timing chain while the water pump is off and out of the way?
is there anyway to safely clean carbon from the engine. i have heard of running deisel through it for a little while and then replacing the oil. i plan on replacing my hoses, belt, valve cover gaskets, and thermostat. i put plugs, plugwires, distr cap, and rotor button on about 30k miles ago. what about cleaning injectors, i am not completely sure how this works.
i know this is a lot of questions...any help would be appreciated.
thanks

I recently began hearing a tapping when starting my 1998 silverado, it doesn't matter if the engine is warm or cold. it goes away after a while. i am pretty sure that it is a lifter losing prime, but not positive. i just noticed my water pump is leaking. it has about 70k miles on it. the truck has 173k miles. it has been good to me. i have never been into the engine before. i am trying to make it last one more year. the intake manifold has been leaking for a year or so, just enough to tick you off. i was thinking of replacing all of it at once. here are my questions--
should i replace all of the lifters or only those that are either sticking or losing prime?
do i have to remove the intake to replace the lifters? (if so i will fix that gasket at the same time)
if the lifter(s) are bad, is this a sign of more problems sooner than a year from now?
is there anything else you would do while you had the engine partially disassembled? what about timing chain while the water pump is off and out of the way?
is there anyway to safely clean carbon from the engine. i have heard of running deisel through it for a little while and then replacing the oil. i plan on replacing my hoses, belt, valve cover gaskets, and thermostat. i put plugs, plugwires, distr cap, and rotor button on about 30k miles ago. what about cleaning injectors, i am not completely sure how this works.
i know this is a lot of questions...any help would be appreciated.
thanks

Well you have neglected a small problem and now its going to get expensive.
That little intake leak thats just enough to tick you off has become a major problem thats going to piss you off.
The coolant was leaking internally also and this is what is causing your lifters to collapse.
You can try to replace the lifters and hope for the best, but in my experiance, you are going to see problems down the road.

Well you have neglected a small problem and now its going to get expensive.
That little intake leak thats just enough to tick you off has become a major problem thats going to piss you off.
The coolant was leaking internally also and this is what is causing your lifters to collapse.
You can try to replace the lifters and hope for the best, but in my experiance, you are going to see problems down the road.
so is that a slap on the hand for neglecting the small problem, or can you answer the other questions instead?
i have monitored the leak, there is no coolant in my oil and i don't seem to be losing any through my exaust. so how would the coolant be harming my lifter?
also the tapping is on the opposite side of my engine from the leak.