Well, after slightly over 300K on the 1989 Riviera I hear the dreaded noise of the Harmonic balancer finally getting ready to let go. I thought about doing it myself but with all the information on this board about removing the bolt I talked to my local Buick dealer and he said about 1 hour labor plus parts I felt that would be safer than me risking life and limb. I parked it until they could get in the shop. They replaced it for $125.00 labor including a new seal. Nice and quiet now! Thanks to all the discussion on this topic I feel I made the right decision. I supplied a new Harmonic Balancer. about $200.00

I too know my limitations. I had mine changed at the Buick dealer. I also asked the technician to check the condition of the crank sensor. He said it looked like it was probably the original. I said what the H#ll. Had them replace the crank sensor at the same time. (Figured it would save me a trip back there in a few months).

had mine done by local wrench with OEM part. not cheap but better than the alternative.part was more expensive than the labor @ 1 hour charge
i was surprised at how fast the balancer went out.
local errands , stop and go , restart at the grocery store and there it was . no warning.
as long as i kept the idle rpm at about 1100 the vibration went away. had it fixed shortly thereafter.

I enjoy the satisfaction of DIY and took the approach of giving it your best and if the bolt breaks free you do the job and if it is too tight then there is a trip to the dealer in your future. Mine broke free and the job was a relatively easy DIY on the driveway.

I'm working on the same issue right now.
Fortunately, mine came off no problem at all.
The trick is to make sure you position and brace the breaker
bar in the correct spot.

I too am changing my crank sensor since mine got damaged, which is a long story in itself. Anyways, crank sensor was $29.95 from Autozone. I decided to replace the harmonic balncer also since my engine has 175K and some of the tangs in the shutter wheel got bent. I'm getting one off of Ebay for $67.99 (Dorman brand / free shipping too)

Kit / 90 Reatta

Kit,
I ordered a balancer from a vendor on e-Bay a couple of years ago, it seems there's a difference in width in some, at any rate, the one I ordered (not from the vendor you're talking about) was too narrow. It's good they show the width measurement, I'd suggest measuring yours to make sure it matches their balancer.

Good luck,

Jim Too