Check that the foam mirror bumper has not turned to a sticky, gummy, mass, causing the mirror to adhere to the focus screen when it is in the up position. I have had several TL Electro/TL Electro X cameras where that was the problem. On the TL Electro, with the horizontal cloth shutter, it is very important to clean up and replace the foam body seals or you will end up ruining your shutter when bits of gunk get stuck to it.