MagSafe isuues: intermittent but mostly never charges.

My MacBook MagSafe adaptor began working intermittently at first then not at all. I checked the connection and looked for obstructions, none found. Checked the depressable pins , all working as designed. Bought a new charger, worked but only charged to 40 % before lights out! Now I have two chargers that won’t light up or charge.. tried several SMC. Resets to no avail. Purchased new MagSafe board and replaced. Still not working. Checked prices on logic board, around $400 plus. Seems too much to invest in 2012 model. Apple wants over $700 which definitely is not worth it. Does anyone have further suggestions of what I could try? Strangely, every once in awhile I will play with the chargers at the magnetic connection and the light will go on and start charging. As soon as it is unplugged and plugged back in, no light & no charge. I have tried with and without the extension cord that comes with the MagSafe adaptor with the same results. MacBook runs surprisingly well and fast for its age. Hoping to salvage!