the letter "L" indicates that the low speed selection on the H/L selector switch for the speed selection for transmission.
Some trucks came with this option and have a switch on the console down beside the steering column that allows you to set the maximum speed of the truck. If the switch is in higher speed mode there will be an "H" displayed in that spot on the display, if low speed is selected then the "L" is displayed.
As far as getting parts for this truck my suggestion is to go to your local cat dealer and request TVH parts (if they are available for the part you want).
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