IH 300 Utility Problems

I recently helped a friend of mine do some work on his 300 Utility tractor, which had been severely neglected.
We had the head gone through, and the cylinders honed and ringed, and installed new bearings, and put back together.
The engine now runs darn good, but has a couple problems we can't figure out.
First, at idle, till 1/2 throttle, there is a loud clacking noise somewhere in the engine, that disappears when the rpms increase. It sounds like a sticky lifter, but have failed in pinpointing the noise. The oil pressure is very good, even at idle.
Other than the noise, it runs great.
The next problem, is I can't get oil to stop leaking out of the tach drive cable head. We installed a new tach drive gear, as the old one was damaged. The O-ring is on the end of the gear, and I even added another to help seal, but still leaks.
Even though hydraulic oil is thick, it leaks out quite alot.
I've taken it apart, and know it is not the gasket behind the gear drive piece. Everything is as it should be. We have another 300U that I took apart to compare, and everything seems the same, almost.
The one with the problem, when I pull out the little housing that holds the tach drive gear, from the tractor, there is a large amount of hydraulic oil that runs out of the hole.
When I took the tach drive out of the other one, there was no oil that came out. (maybe very low on hydraulic oil, but it has a loader, and it seems to work fine.)
Yesterday, to give the tractor a workout, we hooked it to a #47 IH hay baler, and went to work.
The tractor handled the baler like a dream, untill I noticed oil starting to spray out the side of the motor.
This wasn't motor oil, but hydraulic oil, which was coming out of a blown gasket that is between the hydraulic pump, and the distributor drive housing.
So have to disassemble, and replace that.
It seems odd that the gasket would have blown out.
Is there a connection of the blown gasket, and the amount of oil I'm losing out of the tach drive?
I had noticed that when using the tractor baling, the hydraulic lines that run from the pump to the rear hydraulics of the tractor, got pretty hot against my leg. Don't care for that, but may have to add a shield, or insulation, to protect leg.
I'm pretty comfortable around tractors, and working on them, but sometimes one can stump me pretty good, or I've never come across before.
Anyone out there that can help with one or all my problems here, would be greatly appreciated.

There is usually a rubber washer used in the end of the tack cable used as a seal. Yours may be missing..

First, the engine noise. With the engine running
at the RPM that makes the worst noise, try pulling
one plug wire at a time, see if one makes the
noise stop or change rhythm. If so, something is
going on with that cylinder and need to be checked
out before it causes something bad to happen.

If no particular cylinder is making the noise,
look for possibility of loose crank pulley, loose
flywheel, valve train noise (try checking each
rocker with a feeler gauge with the engine at slow
idle) Could be lots of things, use the "long
screwdriver stethoscope" to get a better idea
where it's coming from.

The hydraulic leak sounds like a pump seal
leaking, pressurizing an area that's not supposed
to be pressurized. Can't actually picture how it's
set up, but having 2 problems with the same
component sounds like there is another reason for
the leaks.

Well, got 2 of the problems solved. I had talked to the local Case/IH dealer, and was told that the pump seals do leak, and that they had replaced many of them over the years.
With the seal on the distributor side having failed, it caused an over abundance of oil in the distributor manifold, and to the tach drive cable.
It fixed 2 of the problems, and now I'm down to the noise.
I haven't done the spark plug pull test yet, but do know its not from a loose rocker arm, as I've checked that out.
It hasn't caused any problems, and goes away when the rpms increase. Oil pressure is great on the gauge, so it's not a poor oiling problem.
Thanks for the replies, and if I ever find the noise, I will let all know.