The U Boat crews were mostly very young, sometimes below 18 when they changed their date of birth above 18 to become volunteers.
As you might remember D Day 2015 there were still quite a few veterans. But: the complete amount of U Boat crew members were just only 40.000

That's much less than the amount of 1944 D-Day Veterans. A 1942 crew member should be born before 1924 ... today about 94 years old.

There might be some living german u boat veterans but only a few.
If they want to write?
Most of WW II Vets did not like to speak about their war memories.
And if they had talked it had been to previous comrades they knew quite well - all the other time they @#$%& their mouth cause most of their wifes didn't want to hear the old war stories because these wifes didn't want to be remembered to their bad war memories during air raids or as refugges trying to escape the nearer coming frontier.
They even didn't want to hear stories about the pow time of their husbands in russis again and again. Therefore the vets met their comrades at special meetings of the previous arms.

And finally: vets of an age about 90 years are mostly not able to use a computer or internet.

Good luck !

Wolf