Bad Catalytic Converter

[jda2000]

"the breather box in a volvo is similar to the PCV system in an american car. If the PCV system is clogged, the crankcase pressure is increased and this will lead to oil leaks from engine seals.

Get yourself another mechanic familiar with volvos, get it diagnosed right. I would not replace the cat converter just yet. Most likely the breather system needs a total replacement.