1998 changed a lot of vacuum lines. The fuel damper on your car may not need a vacuum, between intake runner #1 and #2.

You need to take a flashlight and look down behind the engine, on the subframe, at the fuel pressure sensor. The 2 hard lines coming over the engine will go directly to it. Inspect the elbows and follow the line toward the turbo.

One thing you can do is get a latex glove and wrap it around the oil filler tube, without cap of course, with a rubber band. Then when you start the engine, see if it slowly gets drawn into the cam area (good) or if the glove inflates and waves the sign of help (no vacuum).

A diagnostic machine will not pinpoint anything for you. Vacuum leaks are common and almost impossible to trace. Throwing money at it will not make the P0133 go away. Replacing the rear O2 sensor might help, but there is no guarantee.

Slow to respond means that it is working. The front O2 sensor might just be dirty. Or the spark plugs are fouled and not burning everything. But in most cases it is due to lack of vacuum which causes a rich burn condition.

You could clear the code and blow out the carbon... But, I suspect that the code will come back.
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My back feels better when I sit in a Volvo seat