After two new seals - proper volvo ones - and a whole bunch of silicon sealant I gave up and purchased one of these:
https://yoshifab.com/store/turbo-red...rsion-kit.html
That, a 8an turbo chra drain and a custom made pipe (£28 from a hydraulic specialist using the hard pipe as a template) and the problem went away forever.
Bonus is turbo removal is also a whole bunch easier.
If your car is off the road anyway I would seriously consider this.
(Oh, and if you are removing the turbo anyway i'd also do the seals for the oil cooler - they are not expensive from volvo and a doddle to change, plus removing the oil cooler makes the bung a whole lot easier to fit.
My 2c
PP