What improvements would I get with a "better" preamp?

@decooney There are two large gold colored Jensen caps in mine and I know I was told that it had oil caps as well as being direct coupled, having Hexfred rectifiers and mine also is a 98P with Lundahl SUT upgrade. Beyond that, I really don't know if there is anything else besides what made it an F1 in the first place. At some point, I'll probably send it to Cary for a "check up" and see if it would benefit from any repairs or upgrades. I know the Mundorf caps get mentioned and @harpo75  talked about some improvement to the PS as well. He worked on a lot of these and designed a good part of the SLP 05. Haven't seen him in awhile, I hope he's OK. 

Hey billpete.  I’m doing well, I try to stay out of some of this stuff.  You can probably understand why.  
Unless you’re having an issue with yours or you notice oil leaking from the oil cap I wouldn’t worry about a check up.  Everyone at Cary is new now so I really don’t know what they’re doing anymore or how far they take upgrades.  The other tech (Marc) and I came from a long tube background and would really think about how we could get the best sound quality from each piece. I modified my first Dynaco Pas preamp and Mark IV amps and Altec amps back in the early 1980’s and was hooked on tubes ever since.  Along the way I learned more about solid state and digital working with Mike Moffat. When he started Theta Digital I went to work for him way, way back.  I was in and out of audio through the years but it’s always been my first love. Many years of fun! 
I still work on some equipment here and there.  I recently repaired, upgraded and retubed a fellows CAD-805’s for him.  I forgot how heavy those were!
 

@harpo75 I am so very glad to hear from you. Everything in my SLP 98 and it's PS, looks absolutely pristeen.........so maybe there is nothing to worry about. I don't understand when people refer to this preamp as sounding thick. I don't feel that way but maybe I don't understand the term? Anyway, great to hear from you. I may reach out to you with Cary questions from time to time if that's OK. As to getting any of these things worked on, I really have no idea where to turn and hesitate to even involve Cary for the reasons you have relayed. 

From what I understand they have gotten some good technical people.  I just don’t know what backgrounds they have in the tube world.  Please don’t  get me wrong. It’s just that the techs keep changing there.  The young guys don’t stay long like we used to. 
I don’t mind at all answering questions.  I even take on a job here and there.  I’m just careful how much I do now days so I don’t get too sore.  You know, when you’re retired a few bucks once in a while sure doesn’t hurt. 

Hey @harpo75 good to know about you.  Marc and I followed along with each other and after he left and into tube Mic gear and stuff.  We stay in touch on FB some, with similar hobbies growing up.  He helped me in my early SLI-80 and V12R upgrades and right in to the SLP-98. I connected Marc with a local tech nearby who did some amazing upgrades to my SLI-80, and Cary ended up buying that amp back from me full price, they wanted to see it, hear it, and had it in the showroom a while. A customer really wanted it.  I wish I had not resold that one. 

@billpete following along with harpo75, as long as the caps dont appear to leaking and not bulging or anything, maybe you have some of the good batch caps.  if you like the way it sounds now, could be a non-issue and happy listening.

IF you do have a chance to have someone check it or curious to have it upgraded, I can share with you my buddy’s F1 got upgraded at first (caps only) and he really liked the cap upgrades since he wanted even more transparency. He had Harbeth 40.1s, and the midrange did sound a little thick [with his speakers, as I understand it] so that is why he went with different caps in that older F1 style unit.  He eventually ordered another all new 98 with ALL of the latest upgrades. Each case might be unique to each persons gear, room, hearing, and listening preferences.  The downside of that cap change is you might lose what you like now if the current tone, character, body, level of detail, and presentation suits you just fine as-is.

Might only be worth doing any of those upgrades IF you are looking to change the sound in a particular way, wanting more transparency or opening up the sound stage more. One of my friends changed caps obsessively, 5-6 times, and eventually ended up going back to the original caps liking it better. Worth thinking about more. Go with what sounds best to you, all that matters :)