Yeah, the fact that the frost is concentrated on a few components in your photos does NOT tell you whether the cause is low coolant level, nor does it tell you there is a flaw or leak at that particular spot. That is just the location where there is poorest air flow to prevent frost build-up AND poorest heating to melt the frost in the auto-defrost cycle.
ALSO: I forgot an important idea that Torn Mind called up. A VERY common cause of poor cooling in older fridges is the door seal gets leaky so there is constant heat and room air (carries humidity to form frost) entering the fridge. This causes both warmer interior temperatures and fast frost build-up requiring frequent defrost cycles. There is a simple test for this. Get a single sheet of plain paper - maybe cut it to a strip only about 5" wide. Carefully go around the edge of each door in many spots. At each test spot, open the door slightly, insert the paper and close the door. Pull that paper out of there slowly. There should be modest drag to keep the paper in the seal zone between fridge frame and rubber seal strip. It you find any zone where there is almost NO drag, that it a significant air leak zone. SOMETIMES this can be caused by door misalignment in one zone, and you may be able to fix that by adjusting the hinges. But more commonly there are a few leaks in unrelated zones because the seal itself has lost flexibility and can't stick to the frame. (Usually there is a magnetic strip inside the seal). The fix is to buy a new seal. Get the exact one for your fridge, using maker and exact model number, from an appliance parts shop. For most by turning the seal "inside out" you will be able to see how it is fastened in place all around the door. Remove the old seal, install the replacement, and re-test with the paper strip.
ALSO: I forgot an important idea that Torn Mind called up. A VERY common cause of poor cooling in older fridges is the door seal gets leaky so there is constant heat and room air (carries humidity to form frost) entering the fridge. This causes both warmer interior temperatures and fast frost build-up requiring frequent defrost cycles. There is a simple test for this. Get a single sheet of plain paper - maybe cut it to a strip only about 5" wide. Carefully go around the edge of each door in many spots. At each test spot, open the door slightly, insert the paper and close the door. Pull that paper out of there slowly. There should be modest drag to keep the paper in the seal zone between fridge frame and rubber seal strip. It you find any zone where there is almost NO drag, that it a significant air leak zone. SOMETIMES this can be caused by door misalignment in one zone, and you may be able to fix that by adjusting the hinges. But more commonly there are a few leaks in unrelated zones because the seal itself has lost flexibility and can't stick to the frame. (Usually there is a magnetic strip inside the seal). The fix is to buy a new seal. Get the exact one for your fridge, using maker and exact model number, from an appliance parts shop. For most by turning the seal "inside out" you will be able to see how it is fastened in place all around the door. Remove the old seal, install the replacement, and re-test with the paper strip.