Yes, firstly clean and try to get it working.
Most ‘difficult’ regulators eventually get replaced with ball valves. But you have to work out the construction of a housing body to connect the steam feed, the valve and the rotational input from the regulator shaft. This link might show you what others have suggested for a different valve replacement. modeleng.proboards.com/thread/15196/stroudley-regulator-problem
Alternatively, see whether you can replace the valve seats with PTFE or o-ring inserts – sometimes a good fix to keep the original design.