BOAC- That is absolutely right, but to clarify, there are two possibilities depending on wheater the TE flaps are extended or not. If the LE Transit light comes on then you use the LE FLAPS TRANSIT check. Then you decide if the light (or lights) came on with TE flaps extented or not. If it happened with the TE flaps extended you then use the ASSYm or NO LED checklist which leads to a F15 prep. As you say, if the LED subsequently behaves correctly then you can have another look at the snag or lack of.
The assumption is that if the LED Transit light is on, there is a disagreement between TE position and LE positon. Which in the takeoff scenario means that one or more have remained in an EXTENDED positon when the TE flaps are selected up. If only one is out then no big deal. If more than one then you have to follow the limits and the ASYM or NO LED checklist. On the other hand, if the light comes on when TE flaps are EXTENDED when slowing down for approach, it now means the one or more LEDs have failed to move to the required position, which could mean they are still retracted. This is considered more serious hence the reason for the F15 approach irrespective of how many LEDs have failed or not.