All have provided some good advice here ... well, except the part about CV joints, LOL! Once the swivel balls become pitted and worn, there really is no good solution other than complete replacement. If you tear it down and replace ONLY the swivel ball seals, it will still leak.
When you disassemble the unit, you MUST inspect your Railko bushing and tapered bearing and race. These are adversely impacted by lack of lubrication and ingress of contamination. If the seals are leaking lubricant out ... they are also letting contamination into the assembly! Bear in mind that your upper and lower shims are the ONLY means to adjust pre-load for this assembly on a Series vehicle. Not enough shims and you will crush the bearing cage. Many DIY mechanics get this procedure wrong and it is critical to steering and reliable service. Regarding Series steering, this is also your SAI/KPI (or Swivel Pin Inclination in British-talk). If you conduct an alignment prior to your repairs, your SAI/SPI should be around 7 degrees. If not, these components are seriously worn and require replacement. In extreme cases, I have inspected swivel pin assemblies that are so baldy worn that the owner experiences the dreaded "death wobble".
While we are on this subject, I am often asked about CAMBER and CASTER adjustments on a Series vehicle. The short answer is that there are NONE! That being said, a proper 4 wheel alignment should be performed on your vehicle. If your Caster exceeds 3 degrees (+) or lands in the (-), you have some problems. This could mean a bent axle assembly or your axle has shifted due to a broken center bolt on your leaf springs. The later is an easy fix. Cross camber should not exceed 0.5 to 1.0 degree. Vehicle pull will exist if cross camber become extreme. Proper alignment will also reveal if your vehicle has setback conditions. On uni-body cars this is usually the result of a collision. It means your vehicle has a shorter wheelbase on one side. On solid axle, off-road vehicles, 4 wheel alignment will also reveal if your truck is "dog tracking". If your thrust angle has deviated significantly from your Geometric Centerline (either positive or negative), your rear axle has probably sheared a center spring bolt (as above) or your u-bolts are loose or wonky. Again, not a terribly complicated fix.
Much like Caster, CAMBER is not adjustable on Series vehicles. Typical spec is 1.5 degrees. If camber or cross-camber is out of specification, then you have a bent component. CAMBER is the inward or outward tilt of your tire and wheel assembly. If the inside or outside tread of your tires is wearing much faster than the center, then you have a CAMBER issue on your vehicle.
TOE is a steering angle that is adjustable on a Series vehicle. Like most vehicles of this sort, toe is set slightly POSITIVE or "toe in".
I hasten to add that many old Landy's have a rancid, clapped-out chassis ... if that's the case, then all bets are off! Frame buckle and sag are possible ... even broken frames. All of this, obviously, impacts steering, suspension and safety.
So, now you know. Remember to work clean and follow the manuals. Seek professional alignment service (usually not very expensive) to ensure that your vehicle is within spec. Go forth and become greasy!