I've had 3 basenjis, only one had seizures, started about age 15 and not frequently - had increased to approx monthly by the time she was PTS (unrelated to seizures).
I now have some kind of crossbreed terrier, we think she's about 17, and she's had seizures on 3 occasions in the last 6 months.
My first basenji had full blown seizures (lying on her side, paddling, pooing) but they were 3-4 months apart. Vet said until they occurred more frequently, it was better not to medicate. Took her about 4h to recover. A year later they were happening about once a month but she was PTS for an unrelated reason (spleen/liver/stomach tumour - she was 16).