I took an early distribution of $5.1K from my Trad IRA in 1998 for a qualified first-time homebuyer distribution. I have all the paperwork to support this. Can I repay?

If you replace the funds within 60 days of the distribution, it will be a rollover and it will not count as a contribution.  However, if you are outside the 60 day window, it will count as a current year contribution which counts toward your annual amount. 

The deadline to put any of the money taken out in 1998 back into an IRA passed more than 25 years ago.  Any money that you put into a traditional IRA now would be a new, unrelated contribution.