Never actually heard that myself (not until now). I built a T160 out of boxes of bits in about 1982. Took me months but it was great fun (most of the time). I wasn't rich, so it was the only possible way of getting such a fantastic bike on very low money. Luckily it was 99% complete and all very good.
I rode it for some time - not 20000 miles I must admit, but unlike their reputation it never drank a drop of oil or smoked or rattled or missed a beat.
I really wouldn't worry about it - if it's been built properly, and maintained properly, it'll be fine. If it hasn't it probably won't be so good, but watch for the signs and if any show, rip it down & do it properly before it does itself any damage. They really are beautiful machines when everything is right, and it really isn't all that hard to get everything right.