IIRC, the TL used a 1.35V battery, the 675 mercury, no longer available. The new 675 batteries, mostly alkaline, are 1.5V. That might account for some meter inaccuracy, although it certainly doesn't rule out other causes. There's a zinc-air Wein 675 cell with the correct voltage that might work for you, although it's got a shorter life, especially in arid conditons. You can re-use the washer from the Wein cell with hearing aid zinc-air 675 batteries, or you can use the same batteries with an O-ring (#13 ?), or a thin slice of 1/2" CPVC pipe to center them in the battery chamber. There's also a CRIS MR-9 (google it) adapter, about $30 and re-usable, for dropping 1.5V 386 and similar 1.5V batteries to the correct voltage for the camera.

As I said, you may be seeing other effects, but if you have the wrong battery voltage, you'll be perhaps a couple of stops off from that alone, and won't be able to accurately judge meter behaviour.

Lee