89 190E 2.6 Heater Core Issue: Request advice on options of repair.

I have an 89 190E 2.6. There is a leak in the heater core on the passenger side by the gas peddle. In attempting to diagnose the problem I have removed the dash up to the removal of the instrument panel. I am leery of removing this due to my limited mechanical experience. This seems to be a common problem judging from past posts on this forum. I have read of two options:

Remove the dash and replace the heater core, which is not fun.
Prestone stop leak.

I have read of one person (Cargoman) who was successful with Prestone Stop Leak. Has anyone else done this? If so, will this product cause harm the engine? If Prestone is not the answer, how difficult is it to remove the instrument panel? I have taken a look underneath and do not see where it is being held to the dash.

Any advice or past experiences with this particular problem would be greatly appreciated.

Thanks

Ben, I can't really answer your question on removing the heater core, because when I read about doing it (I have a CD Maintenance Manual) it seemed like a job I just didn't want to get into, especially at that time of year (We live in Phoenix, where it gets too hot to work on cars in our own garage). So for me, it was worth a try with Prestone Stop Leak, and it worked. Of course, there are other brands of "stop-leak" like Bars Leak, etc. I just happened to pick Prestone while at my local Wal-Mart because what I read on the container sounded more reasonable and less scarey that what I read on the other brands. But, as I mentioned in my private message to you, I don't really know how long the fix will last, because the car died for unrelated issues a few weeks later.

Lee