I had the exact same question. According to my parts catalog it can take an RCA-121 or a SE 9301 transistor. Then according to a wonderful game plan repair guide, available online. (I can't post a link because I'm new, so you can "Google Game Pinball Repair", and the guide is the url that starts with Level42, scroll down to parts to have on hand)

He states:
"SE9301 or 2N6388 or NTE263 or TIP102 (used on Solenoid driver to drive coils). TIP102's are used in so many other pinball games, I would just buy them. They have the same values except the TIP102 is rated at 12 amps, while the SE9302 is rated at 10 amps."

So I think it's probably fine, and is how I've decided to proceed on my repair. In addition I have several scrap SDU-1 units that I checked that have had some repairs made to them with TIP122's.

Good Luck.