At 85%, $350-ish less parts cost would be fair. If paying a third party to do the work, adjust to your conscience.
There are lots of youtube vids and other resources to R&R the seals. Use a 4' pipe clamp (with trimmed wood blocks to protect the rifle's metal parts and bridge the aft safety tang) to back out the end plug and to replace same after installing new guts. Hang on to the cylinder so nothing shifts/launches. Keep little ones away and wear safety glasses. The usual common sense. It's not hard and you'll know what's what at the end. Zip tie the trigger/safety assembly when removing so it goes back in the same way. Snip it on the way back in. Lots of hints to get you there in my two posts....
May The Force be with you!
