Bryans,
Sounds as though youre in pretty good shape. Maybe a visit to your Linn dealer for a tune up and have the Valhalla board checked out. Most all the comments to save the Lp12 and upgrade are with merit IMHO as it is a matter of what you can get for the money that will sound this good.
I would suggest a new Akiva cartridge by Linn. It is manufactured by Scan-tech who also offer the Lyra line of their own and indeed the Akiva is a well suited cartridge for your deck and arm. It is an obvious match. If you do not, you will need a competent phono amp. Linns Linto phono stage is excellent and the quietist phono amp I have ever heard. Linn has offered a handsome trade value on old Arkiv/Arkiva trade ins to the tune of about 1100.00 USD toward a Akiva. I went this route a couple of years ago by picking up an old Arkiv B on ebay for about 200.00 USD for trade with my dealer and have not regretted it for one minute since. Check out Stereophiles Art Dudley review of this cartridge in which he makes the comments that it is one of the quietist cartridges for record surface noise that he has ever heard and if he could only have a monogamous relationship with phono cartridges for his Lp12, this (Akiva) would be the one to spend the rest of his days with. I would concur.
Linn upgrades to the Lp12 from Glasgow are said to becoming. My opinion is that the cost is outrageous and not competitive in the market place, not like upgrades in their past. Talk of a 5000.00 USD aluminum billeted replacement for the wood surround that we all have and thousands more for a new sub-chassis of some undisclosed material composite, and a refresh of the existing Ekos arm with even tighter tolerances and a material change on the arm tube, again for thousands more, doesnt sound like anything Ill be investing in.
I have had my Linn Sondek Lp12 since 1983 and still find it both competitive and a value today. Happy Listening!