The front pump seal you mention is also the same as the torque converter seal and as mentioned, this seal is not accessible without dropping the transmission.
Question. Did you buy this car new or do you live in a northern rust belt state (MN, OH, etc)? The reason I ask is because you mention 4 stripped subframe bolts which is very odd.
No way should this occur unless they were rusted to oblivion or someone has had the transmission out before and stripped them due to being ham-fisted.
The turbocharger is not connected to the transmission. While it's very difficult to tell what's going on here, is it possible the sluggishness you feel when the turbo did not kick in is actually the transmission not downshifting as it should during hard acceleration and this is not a turbocharger problem at all?
If the problem is legitimately in the turbocharger system, and this problem was not present before, then the problem could be an intake boot clamp loose or something like that. This would allow the intake to lose boost pressure when you're trying to accelerate hard.
Wished I could be of more assistance and hope this helps some.