Auto trans not fully going into reverse

I have a 2000 Golf 1.9 TDI with 4 speed adaptive auto trans and it
doesn't want to engage into reverse. Every once and a while it works
fine but mostly it just barely pulls into reverse or it takes 5 or 10
seconds and a few engine revs before it will engage. Tranny was
serviced about 15k before and fluid is fine. I am thinking a valve is
stuck. I was considering putting in some Trans-x or Sea Foam and see
if it is gunked up but was unsure about this because of the manual
saying to use only VW transmission oil. If I drain and change filter
it says 3.2 quarts of fluid but that isn't going to be my total oil
capacity is it? I would appreciate any ideas or advice.


Thanks,