Electrical – Can a plug melt when unit is not turned on

Any leakage current will cause CFLs to flash. I had to replace my porch light timer with a relay type because the sensor in my original one used a very slight amount of current to test if the bulbs were installed and working. And here's a similar problem I have been having, for which I have not yet found a suitable solution: I have some LED spotlights on a dimmer that ties in to a circuit with two other incandescent lamp system on dimmers. Depending upon the setting of all three dimmers, the LED spots will flash. I think it is noisy contacts in the incandescent dimmers, and that small amount of pulsing is picked up by the LED circuit. It is not annoying enough for me to delay any of my other projects to address it, as it only happens occasionally, and is mostly triggered by the chandelier setting.

Using the 30 A receptacle is a dangerous idea. The internals of the receptacle are designed for a maximum of 30 A, and putting 40 A through it could cause a fire. The receptacle needs to be replaced with a 50 A model (since they don't make 40 A receptacles).

It's fine to have a 40 A breaker feeding a 50 A receptacle. You need to also match the wire size to the breaker rating. A 40 A circuit requires at minimum 8 AWG copper wire, or perhaps thicker for longer runs. 6 AWG might be a good idea. Since you are replacing the receptacle, you should make sure that there is a dedicated safety ground (so four wires are run from the circuit breaker to the receptacle.

Also, I doubt that the old oven died because of the wrong receptacle (assuming that the receptacle is undamaged). However, I have heard of equipment being damaged when not properly grounded (My mom's gas range died prematurely after the installers failed to connect the ground). Double-check the voltages by measuring all 6 pairs of voltages using a voltmeter (Should be 240 between lines (L-L), 120 from L-G and L-N, and 0 from N-G).

Use caution when working with electricity. Don't forget to turn off the breaker (and verify that power is disconnected) before disassembling anything.