Rebuild Beeman Webley Omega .177 800fps

It's been 30+ years and I have never replaced the spring or seals in this old girl. She still shoots but I'm sure she's slowed down some. I must have well over 50,000 pellets through her. I'm conflicted on wether to replace the spring or convert to gas piston. If I stay with the spring do I install an original Webley or go with a Titan XS Mainspring. I also need to find a piston & breach seal. I'll do the work myself, I can replace the springs & seals for about $50 but to convert to piston & replace the seals it would be close to $160. I'm not sure the piston upgrade is worth all that extra as it's not going to increase the MV by much and for a little more money I could buy something with more power. The spring has lasted 30+yrs and the gun has always been very accurate. I think I've talked myself into the spring probably the Titan XS. Has anybody done a replacement spring or piston?