Castrol SRF is the choice of the informed, but as Snjur says, expensive, however less fluid changes, so cost effective and it does what it says on the tin.
I think that you have been extremely unlucky as mechanical failure of Hosetechnic lines is almost unheard of.
However, one failure is one to many and a compensation claim would not be deemed as unreasonable.
It would be a shame to throw in the towel at this stage.
Depending on what parts you require, I have half a dozen 350's in various states of dismantling at the moment, so should have all the parts that you require.
To help you out these parts will be FREE.
Just drop me a PM with what you require.
Alex.
There are various ways to do this job, however my preferred option is to drop and remove the drive shaft. to access the 4 bolts.
It is the quickest and easiest way IMHO.