I replaced a oil pressure sending unit (twice within 2 weeks thinking the first one might have been faulty but its still leaking oil pretty badly. If bad threads or a crack in that port what can I do?

Ok let us make sure where the leak is , spray around the unit with brake cleaner or degreaser and dry off, have a helper start the engine while you inspect the leak , is the oil coming from threaded part of the sender unit or the body part ?. If the body part replace the sender if at the threaded part do the following , check the thread on the unit for damage most have a tapered gas thread , If ok wind several layers of thread tape around the thread of the sender and refit check for leaks. If all else fails you could make a paste of litharge & glycerine but be warned it sets verry hard.

Try wrapping some PTFE tape around the thread incase the thread in block is worn , this will take up any excess space, if still leaks have engine cleaned and look for a leak higher up

The sensor would've had to have been cross threaded pretty badly to score the threads in the block so be certain that's where the leak is coming from...they can be pretty misleading sometimes.

Having said that, if you are certain that there is seepage coming from between the block and the sensor there's a couple of options.
You can try using a liquid gasket on the threading when you reseat the sensor (be sure to use brake cleans to clean the port and threads and be sure it's dry before application) since there isn't a crazy amount of psi and if it's a narrow enough gap it should do.
If that's not enough find a compatible 'stop leak' additive for your oil and use with a new liquid gasket on the sensor.

If that's not enough and you can see where the crack/split/hole you can try bronzing the port and re tap it...but a cracked block is serious business and may be a sign of more serious trouble. Good luck!