I picked up a clean R51 (1829-W1E) for $50 from a local who was having trouble unloading it without Windows. He'd installed the newest Ubuntu but the Unity desktop makes the poor old Pentium M crawl so I installed a lighter distro and it seems pretty happy.

Intended destination is 83 year old father-in-law, who needs a machine for nothing more complex than keeping up with his great grandkids on Facebook and the occasional skype with relatives in the old country. This should be plenty good enough for that and the price is right.

Unfortunately it's got that telltale sign of trouble to come: the pink screen at boot or when waking up from a sleep. Do I cross my fingers and hope it outlasts him (healthy as a horse so not a good bet) or drive up my cost and aggravation by buying and installing a new CCFL (about $20 shipped to me in the great white north)?

Thanks in advance for all good advice.

The fink/red is from a dying CCFL.
It may last, days, weeks, months or even years. Russian roulette anyone?
Unless you are an expert, you will ruin that LCD by trying to replace the CCFL yourself.
14.1" Hitachi and Samsung LCDs are by far the worst for a DIY job.
LG-Philips are not much better.
I now refuse to do any of those.
IDTech and TMD (made by Toshiba) screens give you a fair chance.
Buy a replacement LCD. The XGA are not that expensive.