Volvo Repair: O2 Sensor 1995 850GLT 130K miles, spade connectors, degree elbow

Question
      I was getting a foward O2 sensor slow to respond when I replaced it with a Bosch 15736 universal O2 sensor. I used the quick connect and then replaced it with spade connectors for all four wires. The reason why is that ever 500 miles after I replaced the original, I get a 212 and 436 code from the ECU. I figured that it had a faulty connection on the new sensor, or moisture was getting into the quick connect adapter. The codes are different then when I had the old sensor in the mix. Now it says no forward o2 signal and the rear is over compensating. I don't want to drive around with an Osilliscope in the passenger  seat so what do I do? Also they are not the codes for a vacum leak, I cleaned the vacum tree last week and all the elbows look good. I reset the codes and drive 500 miles and Bang like clock work around 500 miles it happens again. I called bosch to check to see if I had the correct replacement part and they said the front and rear O2 sensor ARE THE SAME I know people have sworn that they are not and that the sensor I have  should work.  
   I don't know what to do next. Replace the Rear O2 sensor, Swap the front with the rear O2 sensor, Replace all the vacum elbows just in case. Replace the gas cap? The codes always happen after 30 to 40 minutes of driving city /highway. I replaced the plugs, wires, air filter, rotor and cap in preventive maintenance and nothing fixed the issue. I get about 25 miles to the gallon and the performance isn't bad for a 168Hp car that weights 3000 lbs. Non Turbo.
Any help you van give would be greatly appriecated. Thanks in advance.  

Answer
ok first look at vacum leak  look around power stering  pump the vacum elbow if you it have going to the intake  90 degree elbow if is broken  2nd  check all vacum hoses around throtle body if all ok you will have to replace with volvo original parts  ho2s front and rear they come with harnes adapters .but check the elbow on the inatke by power stering let me know how it goes  good luck