Tascam 688 sync-to-midi trouble.

[polaro]

Iv'e done the most obvious , and that is following the manual on syncing the 688 with a sequencer.
Now when I push record or play on the 688 the sequencer starts and all. good, great! But, If I record some sequenced audio tracks to the 688, and then want to record some more sequenced audio tracks from the same sequencer, the traacks slightly slide off in time. it is very noticeble.
i've looked everything over. I'm using type 2 tapes. , the 688 is loading the sync clock messages correctly (bar by bar), I use the same bpm everytime.
Is it just that this machine, 688, is old and I'm expecting too much from it.
All I want it for it to stay in sycn, just like midi stays in sync.
Please help, thanks.