The Lightning didn't have a lot of intercooler issues.
The early P-38s (through P-38G) used the leading edge of the wing as an intercooler. It had a cooling capacity of 1,050 HP. If you were asking for 1,050 or fewer HP, you had no intercooler issue. If you were using more power, the engine temp climbed continuously. At some point, it failed. Pilot error, not intercooler issue.
You COULD use more power, but you had to keep an eye on the engine temps, and back off when indicated.
With the P-38J, the intercooler could cool the entire power output capacity of any Allison installed.
Early P-38s basically had 5 issues:
1) No pilot training. They'd cruise into the battle area at low speed, low rpm, and low MP, with gun sights off. If they were attacked, they had to a) throttle back, b) come up on RPM, c) throttle forward, and d) turn on gun sights ... and by that time, they were shot down. It took some real combat flights to sort out tactics like coming into a battle area primed and ready to fight.
2) The early intakes were too smooth on the 3-cylinder units bolted to the heads. It took about 6 months to come up with turbulators to stop the outer 2 cylinders from running rich while in inner one ran lean.
3) British gasoline had a LOT more aromatics (20%) than U.S. gasoline (2%), and they were unable to duplicate the issue (since we ran U.S. gas) until someone shipped over a load of British gas. Once it was duplicated on the test stand, they realized all Allisons were jetted incorrectly for British gas. Unsurprisingly, the early Merlins we ran over here had the same issue in reverse. Once understood, the cure was a simple jetting change.
4) The worst one, as far as crew comfort goes, was the fact that early P-38s used a standard heater muff to heat the cockpit. The air was COLD when it got to the cockpit. A simple switch to an electric cockpit heater solved the issue.
5) The P-38 had the lowest critical Mach number of any major fighter in the ETO, but nobody understood why. Dive flaps helped a lot, but were NOT a solution. In fact, it was never solved completely. Solution would require redesign of the wing-pod and wing-boom intersection.
Early on, the Allison gave trouble over Germany. After the things above were fixed, it would NOT have done so, and proved very reliable in the MTO and PTO areas when it was largely relocated there. You may recall it was the mount of out two top aces. With the P-38L and boosted ailerons, it was a very good roller, even at high speeds.