Most shocks are serviceable/rebuildable whether or not the factory/manufacturer claims that or not. Unless the shocks are quite expensive it will probably be less expensive to replace them rather than rebuild them. I'm not sure what your current shop rate is but mine is $90/hr. Rebuilding shocks is likely to be a skill most regular shops don't have. Fine work, getting very small parts crystal clean. Dealing with easy to damage and difficult to install seals, special tools, etc. Last but not least my OEM E36 M3 shocks lasted well over 100k miles. I would not feel too bad about replacing shocks on that type of schedule.