Hall-sensor replacement for reed switch
Sure, take a look at datasheets for similar size reed switches to bracket the magnetic sensitivity. You wouldn't be able to identify it even if it wasn't potted most likely- they're seldom marked. 

Alternatively, and assuming you're lacking a suitable magnetometer, you could purchase a few inexpensive reed capsules and test the operation distance. Then look at the spec sheets to see what sensitivity makes sense. 

Try Digikey: Product Index > Switches > Magnetic, Reed Switches

I see about 300 products in stock, without searching for size or switching capacity.