My MBP will only charge with a T shaped magsafe now
Technically speaking, you should be using the L-shaped adapter.

As to why it's working with the "incorrect" adapter and not the correct one is because the pins on the MagSafe connector are probably pushed "in" or just contaminated.  Additionally, the pins on the T connector stick out just a bit further than the L connector.

 

You may have some luck cleaning out the MagSafe connector, but in my experience, you have to replace it.

You have a few options:


use the adapter that's currently working
attempt to clean the MagSafe connector
replace the DC in board


Replacing the DC-in board is not "difficult" inasmuch as being tedious and detailed.   It involves removing the logic board because the connector is under it; iFixit has excellent step-by-step guide.

If this is not your cup of tea, I would simply continue using the adapter that works.