If it is a 1/4 watt resistor, dropping down to 6 volts from what is probably a bit more than 12 volts, it will be right on its power limit (12.5-6/150 gives about 40mA, 0.04A*6.5V gives just over 1/4 Watt). If it has an insulating layer of heatshrink over it, it will be less efficient at passing its heat to the air, so will get hotter yet. A physically bigger resistor of the same value but higher wattage rating will cure that problem. Small high wattage resistors are usually made from material that will live through getting VERY hot, and need air space around them to avoid cooking their surroundings, melting plastic insulation and sometimes the solder holding them down while not doing the copper tracking any favours. Bigger resistors have more surface area, so run cooler if the air can get away.
I haven't found the diagram, so just guessing, but the diode is a 3 Amp type, only passing about 40mA, and should not get warm unless the hot resistor is conducting heat to it via the wiring/PCB tracking.