"I suppose it's possible that splicing works fine on MOST cars." it does but must car do not channel their oil leaks to run down the o2 cables into the connectors either.

 

If I replace with new OEM sensors it will still leak on the connector and these "splices" are absolutely liquid proof, three layers of protection. If the sensors don't work it's the sensors not the (my) joint. I see allot of people saying they solder, that may really be a no-no changes resistance values in the wire.