Just picked up a 1985 K100RS that had been in storage quite a while.  Got it fired up with fresh gas and a new battery.  

Took it for a quick spin, but the current plan is to rip into a spline lube job to better assess the condition and to help determine if / how much time and money to spend on this.

Welcome! Just remember - the only dumb question is the one you don't ask. There's plenty of help available here.

Hi Rob welcome to our corner of www. Determining how much to spend can be a very expensive exercise but usually once the bike is running it doesn't run to a great deal.
If you go to the portal page you will find a link to "so you just bought a BMW what now" have a read its full of wonderful reads and good info for a new owner.

Welcome Rob,

Neglected K's left to stand for long periods of time is quite a common theme. I rescued mine from a similar fate and now use her to daily commute and do longer tours - she has rewarded me by running well. There's no doubt that they like to be run.

Your best bet is to do the basics - engine oil, gear and final drive oil and spline lube (slightly more than basic, but straight forward enough). It's probably worth replacing the coolant too (check the radiator filler cap is clean and the seals are good) and of course, if you have time (with the tank off) check the earth point and get some deoxit into all those electrical connectors. Sounds a lot, but easy to do and less than a weekends work and work that will reward you for your efforts. Check your tyres too - lots of posts on that subject but if over 4 years old, change them or she will corner like a pig....

...and then, get out and ride. You will soon know if there are other jobs that need doing and they can be planned in as and when. The real danger is that you start stripping down everything and replace everything and the price goes up and the riding doesn't happen.

Enjoy

Welcome. tip i just learned. make sure you read a whole thread and not just the first page when working an issue. Cheers mate

welcome rob ...sometimes basic measures are the way to keep things going ...for enough time to gain an appreciation,  tyres and shocks are game changers in the handling department ....  which could make a huge difference to how it feels on the road

have fun

First K bike  - Excellent !

First Post on the World's best K bike forum - Brilliant !!! 

Now enjoy the heck out of it.